Well aside from wishing that his wife will make him a responsible man (although rare nowadays) , there is not so much you can do from your side. This man is a already a grown-up. He is used to being spoiled, so from his perspective he is always the best and deserves the best treatment.
Talking sometimes solves this kind of problems. Your friend or another person from the extended family can talk to him. If his reaction gets violent then there is no point of pursuing the discussion, the harm is done. Your friend should not harm his brother even if he gets violent though. There is only patience and duaa that can solve this issue in that case.