[CT] Suicidal boyfriend and abusive mother

I apologize for the length of this, but I feel a bit of backstory is needed:

My boyfriend (a 19 year old trans man) has severe depression with suicidal tendencies and PTSD (primarily caused by his fathers suicide in his early teens, as well as an extremely abusive relationship ~2 years ago), among other things (all undiagnosed, but a 2 year old could diagnose it). We attend a community college and therefore we both live with our parents. He has a history of suicide attempts or near attempts including one ~2 years ago and one last week, where he very nearly jumped off the roof (6th floor) of the schools parking structure and was only stopped by a call to his best friend, who talked him down (my friends and I were trying to contact him and searching for him, but he wouldn't respond).

His mother and older sister are not supportive of his being trans (continuing to call him by his birth name, etc...) and are both emotionally abusive towards him. The only form of help his mother provides are infrequent sessions with his therapist. She does not take his depression seriously at all (last night he told her he was depressed and she responded with "I was you age once, I was sad, then I got over it"), and therefore will not take him to see a psychiatrist.

My question is:

Do his mother and/or sisters actions constitute abuse in a legal sense?

If so, what can be done?

Is there any way to compel her to take him to a psychiatrist?

Is there anything else I can do?

EDIT: He's doing much better, thank you all for your help!