Hey Artchic, sorry to hear what your up against. If I remember rightly your not only stuck with a brother with obvious drink problems, but your mother is an enabler.
If I have that wrong my apologies.
Think you know he can only get help if he chooses to, cld you video him when he comes back at his worst.
Or would this just be a source of amusement for him?
Other than that all I can think is to protect your self as much as you can from getting dragged into his chaos.
Easier said than done, I am sure.

All the best. Stay strong.