I've talked to you in the past about your son's weed problem, and I'm sorry his situation seems to be going south with this mess.
I'm almost more concerned with the warped view of the world your husband and parents seem to have. They'll probably continue to enable him unless it changes.
"this is what young people do"
Are you kidding me? That's absolutely insane. I'm pretty much your son's age as you know, and all of my peers would be labeling someone drinking 24 beers at their mom's house three days a week as an alcoholic. He'd be raising eyebrows if he was drinking that much at a party. Let me be loud and clear that this isn't what young people do.
I'm truly sorry. I don't feel like there's much advice I can give with this situation though, as alcoholism is moving a bit beyond my experience.