you've got an ace up your sleeve with the marijuana use. you might not be able to prove alcoholism, but you can prove drug use. a hair sample will prove that, even if he hasn't used in a while. however, it sounds to me like he's a pot-head since he wanted to grow it in the basement and you found his stash, even tho he denies having any.
Using a hair test, they can find THC for months afterwards, and alcohol is not viewed as harshly as marijuana, but marijuana is still completely against the law.
Keep this in mind please.
and, my children did not want to "tell" on their dad. i hope your son is able to do that.
Beth