Tell your aunt that it IS NOT your responsibility to care for your brother ... It's HIS responsibility.

If he refuses to attend meetings, counseling sessions and take his medications, then he'll just have to accept the consequences for not doing what he knows he's supposed to do.

How in the heck is that your responsibility?

Feel free to show this to that aunt.

If she's so concerned about his welfare why doesn't she provide him with shelter?

Again, don't allow her or anyone else to guilt trip you into doing anything you aren't comfortable doing.

Period!