the baseball bat next to my mother's bed was not within grabbing range....
Bro, I'd have a serious conversation with your brother, while he's not been drinking. You can sympathise w/ his health situation, and tell him that your sorry that life seems to have given him a very raw deal.
BUT, but that his drinking has got to stop if he wants to have a relationship with you. Thenn he'll throw it back at you that you do and other shit that you've done, so be it, but YOU don't talk to yalls mother like that. I'd just tell him that he's not the same person when he drinks and that's fine if he wants to stay that way, you don't have to be around him. But your mother does, and that type of behavior isn't something that you can ever look over. You'll always love him, he's your brother, but you don't have to like him. If he treats your mother like that again, or you hear of him doing it, there's going to be consequences between you and him. period. end of story.
Ask him if you can help him get the help he needs, anything that will stop his behavior. Let him know that you are will to go to any length to help alleviate the problem before it escallates any further.
That's my 2ml, hope it all turns out for the better.
Alcohol never helped me out in any way, the few laughs I had in the earlier years didn't hold a candle to the gallons of tears later in life.