If your aunt and uncle are so concerned with your brother, it sounds like they need to open up the doors to their own home and welcome him in! You are right - you can't stop your brother from making bad choices. If your uncle thinks that he can do it, let *him*. If he wants to nag someone, it sounds like he should be ranting at your brother, not you.

Can you just not answer the phone calls from your aunt and uncle? It sounds like you have so much on your plate right now. I can't imagine having to deal with phone calls like that on top of it.