So sorry to hear about this! I am one who likes their own space, so I can so relate to your brothers frustration with this. What a mess! :(
Are you in contact with your brother now? I think I might suggest that since he is going to counseling already, to ask his counselor to help him with establishing boundaries. What does his wife say about the situation? Is she willing to go with your bro to see the counselor?
2 Timothy 2:15
Do your best to present yourself to God as one approved, a workman who does not need to be ashamed and who correctly handles the word of truth.