I am sorry you are having trouble with your son. There are lots of parents here of teenaged and twenty-something addicts, using, recovering, and not-so-much recovering. I am the mother of a 19 y.o. RAD. Heroin was her DOC. She's been clean since late June 2012. It has been a rough ride but I am really proud of her sobriety.
My first concern is that you and your wife are not on the same page. Perhaps she'd be willing to read some of our stories--all collected here to connect with and learn from--and perhaps she'd see that she is prolonging his recovery by her rescuing and enabling. Many of us are addicted to our addicts, and equally addicted to our fears of putting them out, so we are in need of recovery, too. Maybe you two could attend a NarAnon meeting in your area?
How does he fund his drug use? The computer games seem like a real bonus--what incentive does he have to change his ways? My daughter had to be put out of both her aunt's house and my house before she took her recovery seriously.
What a shame for your marriage to suffer, and for your other two boys to witness this troubling behavior on all sides. My 15 y.o. daughter is still recovering herself from her sister's near death by overdose, and has what I consider PTSD as a result. (She has been going to Alateen and getting a lot of support that way--I highly recommend it.) Please take their mental health as seriously as his drug problem. He's 20. He can make it on his own now.
Keep reading here, and keep working the program. It helps so much.