1) Are they affected by (illegal) drugs or alcohol differently from humans?
Semideus can be effected by drugs, toxins, and alcohol though it's five times less potent than on a human of equal weight/height, and clears from their system five times as quickly.
2) What are the different forms of structure in the siren communities? And is there a sort of council/diplomatic agreement between the different siren's?
Historically sirens have been pretty territorial even with other sirens of their own type. The Hebigumo Foundation constitutes a change from the norm in that way, because the Encantado and Jorogumo who make it up came together for a single cause, rather than because of any affinity for each other. They don't have a council or diplomatic agreement any more than two random people meeting on the street might, and this is because siren communities are as varied as human communities. They can take on a number of different shapes from business partnerships (Hebigumo Foundation) to friendship, alliances, etc. Really though the base unit of siren communities are families - usually small groupings of them scattered all over the place with no real goal other than to survive and thrive in a world that has become progressively more human dominated.
The only 'distinct' community differences which are exceptionally different to humans are the Jorogumo, who tend to be very 'alien' in the way they think compared to humans. They are the only sirens, for example, who would eat their own young if sufficiently starving (especially the males, I imagine). Similarly, they have matriarchies ruled by very strong female Jorogumo mothers who essentially set the rules and enforce them through strength and seduction.
3) How early in life does it become apparent that a child is a siren? What are some ways it manifests?
Most sirens have visible signs of their type either at or very shortly after birth, such as extra limbs, extra eyes, feathers, talons, wings scales and tails. For this reason, male sirens tend to steal their children extremely early on. Usually at birth if they can.
4) Any allergies - or idiosyncrasies that effect how they interact with other species?
I'm inclined to say no. I imagine sirens (and semideus in general) usually adapt pretty quickly to their surroundings and don't really have issues with things like allergies. That said, they have a natural affinity for the wild, so they probably don't like staying in cities for prolonged periods of time.
5) Do sirens appear in mirrors as themselves or is there a quirk?
Their appearance in the mirror reflects the form they are shifted into.
6) If a siren reproduces, how long is the gestation period? Would there be anything usual about it?
The gestation period is roughly the same as it would be for a human, and the only real difference would be a very strong heartbeat or other clear signs the baby is healthy - assuming it does not miscarry early on (first trimester loss is very common for siren/human mating).
7) How many forms does a siren have? Is it a human, a full animal and an in-between or just human and one of the other two?
They have a human form, their natural form, and some have a war form which is like an amped up version of their natural form. None of them turn into full animals.
8) For the lovely spider people, is there a certain 'spider' they take after in their natural form, or can it be any species?
Any species, though this does not impact them other than aesthetically.
9) Are they (all semideus) able to lose limbs? If so, do the regenerate like vampires?
They can lose limbs and regenerate them. For sirens, they regrow them over time though other types of demifae may have different ways of regenerating (the way different paths have different means of regeneration).
10) At what rate do the Sirens age? Is that different for the different kinds?
This one is a bit tricky. Sirens tend to age about the same as humans. Sometimes this slows once they reach maturity. Sometimes it outright stops. Sometimes it picks back up again later. Sometimes they stop aging at a later point in their life than other Sirens. Nobody really knows why.
11) Are there different 'fae' languages for each species or do they all speak just one common tongue?
They don't really speak the fae language any more than humans do. Some semideus who are attached to one of the fae may have access to what pieces of the language means, but it's more like a combination of a dead language and a programming language than anything else.
12) Do the semideus pick their own 'human form' and if so can they change it? Or is it something they have no control over and they are stuck with luck of the draw on appearances?
I'm inclined to say they have no control over it. It's just a humanised version of their natural form.
13) What are their life cycles like?
The lifecycle of the sirens is similar to humans. They're born, hit various milestones (such as harpies learning to fly on top of how to walk), hit maturity, search out partners for reproduction etc. The main difference is the biology, community, instincts, and that Sirens generally stop aging. I'm hesitant to cement too many things aside from that though.
14) Are they born as a live-birth human, or as an egg (as all of the species available are linked with animals that lay eggs), or either, depending upon the mother's species?
Human mothers give live births, siren mothers lay eggs, though usually just one. Sirens have a very low birth rate and a lot of times the eggs don't fertilize in either case, or the young don't make it to term (or hatch).
15) At what age do they reach sexual maturity and begin their quest to reproduce?
I'd say their sexual maturity is similar to humans, but but it doesn't really ramp up until at least the age of 18.
16) Do they ever reach a certain point in their lives where reproduction is no longer a priority, or even possible? If so, what sort of motivations do they shift their focus to?
Not really, no. Though reproduction doesn't necessarily have to be their sole focus or motivation, it's just a very important one.
17) How many offspring do sirens aim to have?
Varied. Biologically speaking, they have a strong imperative to breed as much as possible, but they may not consciously want a lot. It just depends on the individual, it's the biological component that doesn't change.
18) How long is their lifespan?
Potentially infinite, though they can be killed. It's just very very difficult to kill one.
19) How old are Siren PC's allowed to be? What is the canon reasoning behind the limitation, if there is one?
This is a really good question. I'm inclined to say (for fairness) that any siren PC must be within a normal human lifetime). I. E. They should be no more than 80-100. That's mostly just because there are limitations on the ages of most vampires and playable humans, and we want to keep things fairly even.
That said, we may eventually hold contests for ancient demifae the way we have with vampires and humans in the past.
20) Is there a certain social stigma among sirens for what species their mother or father is? (In other words, does it matter in their society which of their parents is siren and which is human?)
No. Any siren baby is precious, given their rarity.
21) Is there a possibility of sirens reproducing with other sirens? Vampires? Any of the Superhumans? Do any of these pairings produce other species than sirens or fadebeasts in the case of vampires?
They could reproduce with classed humans I think with the possible exception of blood thiefs if the blood thief is actively feeding while pregnant (in which case it would miscarry). They can't reproduce with other sirens or vampires at all.
22) Is there any sort of clash between the different sorts of sirens? Any tension or division that could spark conflict between them?
None that are pre-existing (at least not on a wide scale, such as harpy versus jorogumo), though sirens have been territorial in the past. There's no historical context for them to dislike each other though no, and no innate enmity there. Individuals are another matter, of course, depending on how they're plotted and written.
In fact, sirens have been known to be extremely jealous when it comes to mates, and they have been known to kill people for encroaching on their breeding territory, so to speak.
To that end, Sirens likely tend to do something to mark their mates in some way - be it physical markings, scent etc. Sirens of matching type likely respect those limits unless a human proves to be an exceptionally good breeding partner. But across type lines (such as Encantado versus Jorogumo), those possessive markings/claims probably mean less. So I could see that resulting in major quarrels - though again that all comes down to individual sirens and their choices.
23) What sorts of things do each of the sirens view as power? Strength? Wealth? Knowledge? Family? What qualifies a siren as leaders among their community?
This is like Varys's power riddle from Game of Thrones XD The answer is roughly the same - power resides where people believe it resides. So there's not necessarily any one answer to that question. Each siren may value any of the things you listed differently. Some sirens may see a display of might and fear it - where others may see it as a reason to stand up and take arms etc etc.
As far as what qualifies a siren as a leader - that's dependent upon the community structure to which they belong. A family may be run by a mother, father, grandparent etc. An alliance could appointed leaders etc.
24) Is there a social stigma attached to sexual preferences among sirens? Anything they consider inappropriate or taboo?
I imagine sirens class sex with humans different to sex with other sirens. Sex with other sirens can't result in reproduction, so I imagine the rules there are essentially unlimited. Do what you want. However I think there's the expectation that they will try to mate with a human of the opposite gender and I could see other sirens giving some odd looks if they didn't. This extends though to more than just homosexuality, as a siren who has never tried to reproduce would probably also be looked at strangely.
If I'm recalling correctly, my story character Jorogumo was barren
(a curse I need to add at some point), and it caused her to be ostracized by a lot of her family because there was something
wrong with her. So I imagine there might be some of that. It's less about sexuality and more about the 'sacredness of life'. At least according to any sirens who believe that line of rhetoric.
25) What sorts of things are considered criminal among the different sirens? Murder, obviously, is no big deal to Jorogumo, but with their value of wealth, what about thievery, fraud, etc, etc?
I think the law of the sirens is based on might. A Jorogumo who values their wealth could tear another Jorogumo who tries to steal it (and is weaker) to pieces. Or arrive at an agreement with them. I don't think they have a central governing body or means of enforcing laws the way humans do, so it's all very much based on what an individual siren values and what they can do to protect what they value. Or, what a group of sirens working together decide to value, the rules they make for themselves, and how they enforce those rules.
That said, I imagine they're more strict/severe/harsh with 'outsiders'. Outsiders being anyone outside of their group - not necessarily humans or different types of Sirens.
26) how are these sorts of offenses punished? Are they more likely to be banished, imprisoned, executed?
See above.
27) Do any of these things differ among the different types of sirens?
I picture the Jorogumo as being particularly vicious in protecting what they value (be it their own lives, their children, or wealth). This is because they don't really think in a human way at all, which may have something to do with their more arachnid instincts. They also tend to be generally more predatory than other Sirens (though there are always exceptions). They tend to lack compassion, rule through strength, and seem extreme in terms of violence by human standards compared even to other Sirens.
For this reason, Jorogumo communities do tend to be a little different to other siren communities.