Transgender brother..I'm at a loss

So long story short (because it really is a long story).. my brother has decided to become transgender- which I'm 💯 percent fine with. However, my family and I are not totally sure he's making the right choices since he has some severe mental issues. I'm not sure if he's been diagnosed or not-my moms never shared that with me. But he's not all there, never has been since I can remember being kids. Anyway he had a rough (ish) childhood- in his eyes anyway. My parents both worked full time and because of his issues my dad never spent time with him. He has a lot of resentment that he's actually gone out and "found a new family" as in, calls some of his friends mom and dad, has brothers and sisters. Like I said, he's gotten in with the wrong crowd and he's just not all there. He won't return my Gramma's calls, only talks to my parents when he wants money. He's always been extremely selfish and disrespectful. He moved out last spring. My parents don't care that he's transgender it's the way he treats people that they have a problem with. Where do we go from here? It seems like my mom is really upset by this whole situation and I want to help but I don't know how... any advice is welcome! Thanks ladies.