You should also you must determine if there is substance use and abuse involved. This changes the dynamic. If so, you have to focus on healing that first. It depends which drugs but some are very toxic and fatal.
I would not argue Hashkafa at all, but just invite him to all religious events as normal whether he goes or not. Get him Seforim also that may be of interest, not Gemara per se maybe books by Rabbi Twerski also, best of luck, please let us know how things go.