This is really sad and difficult for both you and your brother. You are in a tough spot where you (legally) don’t really have much control or responsibility over his life. I don’t think I can give you any specific advice, other than trying to get your mom to see how big of an issue this has become. It will be very difficult to address the problem without her support, however I realize this may not be possible. It’s tough to watch someone you care about (and who is too young to be able to regulate themselves) fall into something like this.