Hi Darkness,
I am sorry to hear that he distrusts the field of psychology in general. What about the field of substance abuse? It sounds to me like both parents are using. Using substances has been linked to psychological and physical abuse. Not all substance abusers are mentally ill, therefore, you don't need to mention mental illnesses.
Substance Abuse and Domestic Violence: Causes and Interconnections
The above seems to be reputable because it refers to research done by other people. At this point, I think the best thing for him to do is to find alternative housing such as the YMCA or housing for domestic violence victims.