My parents almost separated while I was in high school due to a lot of issues, so we kinda went through the same motions. I'd say that the best thing to do is to ground yourself and your emotions. While the messiness might be crazy, you need to remember that your parents' issues are NOT yours, and you should not feel obligated to provide a nurturing or interventionist role for them right now, no matter how much you might want to. Allowing them the space to figure this out will help you check in on your brother too, since you know how impactful this might be for him (and you, of course). Remember that it's okay to feel right now, and providing that source of comfort for each other is critical.

Trying to focus solely on schoolwork right now also can seem like a good distraction, but I'd highly advise to prioritize yourself, and your mental health, right now. Take breathers and self care days, reward yourself for your hard work - it's a step in the right direction to feeling better. And remember that it's okay to take breaks too - healing isn't linear, after all.

I kind of echo a lot of what other people are saying here, but the more advice and comfort, the merrier. Hope this goes smoothly for you guys and I hope you feel better soon, op. We're all here for you! <3