Infodump! It's what's for dinner!
Nathan is the first-born, favored son of the Petrelli family. He'ssomewhere in his late 20s because having a live canon SUCKS sometimes and his background is what was established for him on the show: he's been a pilot in the Navy, he's a lawyer, and he's worked for the DA's office back in New York.
Where he veers from canon is that he's younger, hasn't yet married or had kids save one, ooops, hasn't yet run for Congress, but he does know that he can fly.
Nathan has aspirations to one day be president. That, combined with what makes a Petrelli a Petrelli, means that he's very aware of public image and a need to keep some things - like superpowers - a secret. This is why he tends to speak in carefully chosen words, and why he'll treat anyone who suggests that he can fly as though they're crazy. Even when one of those people is his brother Peter.
Though encouranged by his parents to be a go-getting overachiever who should believe that the ends - no matter how horrible - justify the means, deep down he's kind of a softie. He's still morally grey and fond of keeping secrets, but he believes he does what he does for the right reasons.
Key points for interacting with Nathan:
1) Though he'd like to keep things a secret, his mind can be read. So anyone with mind reading powers is welcome to go ahead with that. Just please check with me before having your character do anything with the knowledge that Nathan can fly.
2) Likewise, Nathan doesn't yet know that Claire is a version of his daughter. There's plans for how this is going to be revealed to him, so again please check if your character knows/has the ability to know that before Nathan and Claire do.
And I think that covers the basics.
***
Peter is the (as far as we know) second-born, less-favored son of the Petrelli family. All you need to know about his personality can be summed up in that he and Nathan were flat-out told that Nathan was the favorite one, and to all appearances Peter took this in stride and loved his family anyway.
Where Nathan is type-A to the max, Peter is all heart. His default is to believe the best of everyone until they prove otherwise. Once they have proven otherwise he can be quite the pissy bitch about it. This is because Peter can be a huge drama queen.
Peter's power is to copy other people's powers. If you haven't yet, please ping in
here to let me know if you're comfortable with him being able to copy your character's powers or not. I never have him copy without OOC permission, but pinging in there helps me know who not to bother by asking, and also helps me plan plotty stuff when it comes up.
***
Yes, the brothers together are their own entity. Here's why:
1) Canonically these two will go to insane lengths to protect each other. Nathan nearly killed himself to save Peter (and the world, arguably a side-benefit in Nathan's mind) and Peter nearly destroyed the world because all a bad guy had to do to gain Peter's complete trust was save Nathan's life. In other words, the easiest way to get on the boys' bad side is to hurt their brother. Especially Peter's bad side since, again: drama queen and pissy bitch.
2) They touch. A LOT. Like "Winchesters have serious competition" a lot. Like even the cast and crew joke about them making out a lot. Like we have seen them hug, kiss, and caress one aother far more than many unrelated heterosexual couples across the TV landscape. I mention this because every time the boys come together in Fandom I worry that folks may read and think that incest is on the way. It's not. I swear. It's just you can't write Petrellis without the touching. If anything, I try to tone it down from canon. Much though it is pretty
***
If you know Buffyverse canon, then all you need to know that Willow came to Fandom when her "Will be done" spell in s4 went wacky. If you don't know Buffyverse canon, then all you need to know is that she's a witch, she's fairly powerful, and she's totally in love with Peter Pevensie. She also owns a hedgehog named Philbert, and she's kind to squirrels.
***
Angel's a vampire with a soul and not huge with the talking. He's currently an alumn back in his own dimension where he's got his own detective agency staffed by
fates_jaye and
psycho_jackass. He's in love with one (Logan) is fond of the other (Jaye) has a dog (Sean) and really isn't into making new friends, so odds are new people don't have to worry about interacting with him unless they're friends of his friends.
***
And I think that about covers the basis. Feel free to bug with questions/comments/pie. =)