I apologize I made inaccurate assumptions. I stand behind however my query about his behaviour having been enabled. I appreciate the difficulty you are going through regarding his irritating and inappropriate behaviour but this does not sound like a mental health issue to me. It seems behavioural which would be a learned situation as opposed to a lack of control owing to illness. Again, I recommend that expectations be set - in stone - regarding his behaviour when he comes home. Make it clear that you and the rest of the family won't stand for his outburst. Observe his reaction however. If he were to react with a surprise and complete lack of understanding regarding his actions, responsibilities, and consequences then that just might indicate a deeper problem.

For example. My step-son is as sociopath. He could not link cause and effect regarding his actions or his responsibility for them. A common reaction from him when being spoken too about some transgression was to ball up his fists and with a clueless expression demand to know why he was getting in trouble. He could not link his behaviour - ie. theft or violence - with resulting discipline.

If your brother behaves similarly then that definitely would be a problem.