Okay, the four links scared me, but I'm gonna give it a go!
First off, Cole!! I mean, top down, duh…
His personality flows smoothly, but I think you could benefit to add a little more! As the MC, he should definitely have more flaws, as well as a more in-depth personality type. Little blips across the board can add to the humanity. This is a good level of depth for a supporting character, but I would definitely recommend more for the MC!
Hmm, no politics? I see this all the time, and I always say the same thing: I find it very helpful to rate characters on a scale of liberal-ness! It's weird, but really helpful.
Nice work on his backstory! You did a good job setting the scene. I would, however, add a bit more into why they suddenly decided to let a random teenager build herself a house on their property. This seems entirely unrealistic and needs a lot more support to uphold!
I'll overall at the end, so I'm going to move to Hunter! Top down (duh)…
Not bad on the personality page. He's also an MC, so the same critique flies: add some more detail! On a more specific note, I would refine his prejudices. Does he dislike the upper class for not accepting him?
Again, politics! This time it's more important, as you said that he was very opinionated. Politics are an easy place to have a huge opinion in!
Backstory is, again, very nice. I have two notes on this one. One, there's magic all of a sudden! This seems to be very important and thus deserves a place in the backstory. I'm assuming that the magic has a couple plot points–add one or two in! Two, Jasmine married him at sixteen? I originally thought that this was a modern world, but now I'm starting to lean towards fantasy. Even so, sixteen is crazy young to get married! And if this is fantasy, work harder to specify that earlier on. I was going through my critique thinking that this was modern day!
Wait, now I read his clothes and it seems modern again. I'm lost! Ok: if it's modern, sixteen is WAY TOO YOUNG. If it's fantasy, sixteen is still pretty young–I would probably bump it to eighteen, but that's just me. :)
Next! Seth. Top down (why do I keep saying this?)…
When it comes to personality, I think this is an appropriate amount of depth for a side character. One note: he seems kind of loaded with magic here. Make sure not to make him too powerful!
Again, politics–this one isn't too important, since he's, well, a demon, but being non-binary I'd assume he'd lean liberal.
With backstory: it's good in the sense of his creation and his relationship with Talia, but I think there's a lot of unnecessary detail in here. You don't really need to include the entire torture scene in the backstory.
Finally, Tristan!
Give him some prejudices! Everyone has some. I do have one major note here: the whole "sadistic, demonic, torture-and-kill" villain is kind of… stale. See, I understand that he's not human, but I don't think you should leave him to be a flat character. Round him out!
I like the backstory!! I would, however, add more for this decisive "before-and-after" that has been mentioned multiple times. I can infer a bit of it, but make a clearer split!
Overall, these are good characters! Just get a little bit more in depth with all of them and I think you should be good. I'm sorry for the short critiques, but you know, four. ;P
I hope that this helps you!! :DDD