Put him up for adoption (I kid I kid)

I’d get him some therapy, not just the gender affirming kind. And if he’s already in therapy, I’d ask to have a session for both of us where we discuss what happened. I’d probably also put him on punishment. When we were teens, my brother once had a similar outburst (not the “daughter” stuff but the screaming and cursing and telling our mom to get out of his room). We had music lessons to go to that same day, and when we got back home, my parents had taken all of his non essential items (tv, computer, video games etc) out of his room and told him he would get them back when he either could pay them the amount of money they’d spent on the items or he learned to be respectful. Idk if I’d do that exactly, but it seemed to work for my brother.