You are doing enough. You're only one person and not a professional, remember that.
I know you said it wouldn't be good for him to be separated from his family but if they're urging him to kill himself, that's inexcusable. I don't think calling CPS would be a good idea either but it would probably be good to try to keep him out of his house as much as possible. A year and a half is short but can feel like forever, remind him that it's not and he'll be free once he's done with highschool.