I believe he really needs intensive help, and although my parents agree, they never hold my brother to any boundaries or accountability that would actually get him to seek help.
At this point, I'm thinking your best strategy is to focus on that the fact that what your brother and your parents do is outside your control, and the only thing you can control is how you react to them. Try to focus on your own well-being and surround yourself with positive people (friends).
Welcome to the community.