I have recently been having a family issue of my own. Luckily, where I work, I can call up resources for living and talk to a councilor if need be. It really did help me try to deal with things.
One thing I was told, that made the most sense to me, is that you need to make boundaries. It is important because otherwise people like your brother and my mom will exhaust you. Its not any fun. I also helps to realize, that while he is acting very childish, there is nothing you can do about that. The most you can do to help is to use your relationship to influence him.
If you guys have to say no to him or set a boundary to protect your own well beings, that is perfectly fine. It sounds like his actions are already taking a toll on your family.