Aggression and law enforcement

We’ve had issues with our oldest of three children, who is turning 16 years old. At its worst, it involved him getting physical and ending with him being out of the house during a child protective services investigation which lasted a couple of months (staying with his grandparents).

Although he has not gotten physical, since then, he gets very angry, disrespectful and verbally abusive. He also refuses to leave our room at times, demanding his phone and saying he will stay there until 4 AM knocking until we give in.

How can we work on boundaries, without involving calls to law-enforcement, if he begins to show aggression and overstepping boundaries? I am early into learning the rules of teaching under self government, and I thought rather than locking our door at night, next time he comes in (if he does), I am standing ready with a dry erase board to try to teach! I’ve also realized it seems like when his Younger sister and brother are present, it keeps him at Bay because he has more people watching (perhaps he doesn’t want to behave so poorly in front of them).

When do you consider calling law enforcement the right solution?

Thank you so much!