he then adds that it is unethical and illegal to suggest he will lose his liscence if i testify about his drug use.
That part is what I said before, we have similar bar grievences all the time. Be prepared an addict can be fueled to stay clean by teh excitement and drama of whatever, for him his new addiction is hurtinga destroying you and I bet he's been completely clean through this cycle so theres no proof.
Scary too, I bet he's convinced your daughter that the violence she saw and got invovled with was nothing. This creates 2 problems, one no witness but worse she has conflicting emotions that it was okay (where do most abused adults get those feelings from? what they see as kids, just like his father told you there was nothing wrong with grabbing someones neck)
I am really concerned at this point what your lawyer is telling you and I hope his conduct hasnt been in anyway unprofessional. By any chance did the kids give a statement the first night of violence? Did you save messages and emails he sent when angry and confused by it all?
Whatever you do you cannot react, you must for your own best interests stay calm.