Hi
As explained above, all USCIS needs to see if that the protective order, and other related charges indicated on the police report were disposed of, and that it did not involve children. You are overthinking it, to be polite, writing a letter saying he is/was mentally ill and was assaulting his mother really doesn't seem like a good idea. The fact that you are aware of it and know the details is important but that is handled at the embassy interview. They will ask you if you are aware of it and will ask you to show them a copy of the paperwork
For the new drug charge, that does not disqualify him, so if you can get documentation to prove that issue is disposed of, my guess is that you'd be preventing a future issue or delay by enclosing that too and stating this happened after you did the I-129F. Though, probably you'd be making a new delay as they would need to pull his FBI record again. But again, that's my guess, and you'd be advised to get real legal advice and consult an attorney with experience dealing in this rare specific sequence of events,