I had a similar issue with my son’s biological father. He was just in denial that there was any issue whatsoever. Getting a diagnosis with his involvement was painstaking. Not knowing what state you’re in, that state’s laws, or the wording of your current custody paperwork, I can’t say what you need legal wise. However, I can say that I had wording put into our custody paperwork that said we would both follow the recommendations of medical and mental health professionals. So even when bio dad completely disagreed with me, the doctors, the assessments and the treatment plan, it did not matter.