I'm glad that you are taking good care of yourself, and that you know you need to choose your own safety first.

Your family needs to stop mistreating you. Is it possible to reduce your contact with them, can you tell them to stop with the blaming, and then give them consequences (one consequence could be that you limit contact) if they won't listen to you?

One way to reduce distressing worry about your brother would be to limit contact with him too. Maybe you could have a prepared message, a script you have practiced, that you could tell him every time he writes something distressing. You could tell him over and over again that the proper place to take his concerns is professional help, you could have ready a phone number, name of a clinic, etc.

That way you won't be triggered over and over again by trying to figure out if he is safe, what exactly is going on, things like that.