Litmus test #1 - obsessing oveer the problem/person
Litmus test #2 - trying to cure or fix the problem/person
Litmus test #3 - sacrificing your own self or your family for this other
Litmus test #4 - "knowing" the right answers/fix
Litmust test #5 - taking too large a role - taking charge or control of the whole thing
and getting angry when your choice isn't the one made in any of the above.
I think your brother is at his wit's end, and he is wanting support. Support doesn't have to mean jump in feet first up to your shoulders.
Everyone else is giving you good advice, IMO. I wish you the best,