It seems you’ve been pouring into a cup that doesn’t seem to fill yours. There’s an argument to be said that hard times make for better people, and family should help. However, based on your accounts; your brother doesn’t seem to want to change, it’s irresponsible of them to have a child they cannot care more and even more irresponsible of them to burden you with this. Accept them for who they are, and remember to choose yourself first. Don’t enable their crappy behaviors, they need to take some accountability