BWB, Your brother seems to be out of control.If he cannot deal with mom then stay away.Once he sees that his way of dealing with her is upsetting he needs to learn to see things as she sees them.He needs to get in touch with her reality and check his at the door.Remind him this is not about him and what he likes and does not like.Does he consider mom does not like where she is mentally.
Tell him , the next time, there will be two hits.You will hit him and he will hit the floor.
Tell him to educate himself to mothers condition.Then go to church and ask for forgiveness.
Remind him he never knows what tomorrow will bring for him.
Maybe he should write 500 sentences saying I must show mom understanding.That is what I did with my kids, even as teenagers.
Tell him to wake up and smell the coffee.