"What would you do, if you suspected that a family member was becoming ill enough to harm himself or others, and he refused treatment"?
Umm....the last time I checked, this is still America. The family member has done nothing for you to have to "DO" anything about. All you have is suspicion, and you can't protect everyone from everything. Sometimes bad things happen to good people. It's called life. Also, from a legal standpoint, since the family member in question has committed no overt criminal act, your suspicions have little merit.