The 4th and 5th step in AA can be a great help, I agree with Satit, find a professional 5th step person.
Even if a person trys alcohol, many cannot become alcoholic.
He may be abuseing alcohol, but with alcoholism in his biological family
i would suspect he is an alcoholic and should try rehab first.
I feel alcohol may be making the PTSD disorder worse.
See if you can call an addiction counselor and ask if getting rid of the alcohol might help cope,