Hi...
I'm sorry your family is hurting right now. I agree with Peaches, that if SIL said something it was very hard for her to do...
An Al-Anon meeting would be a good resource for you & your family.
Alcoholism is a progressive disease... but being an alcoholic, or at least my understanding of it, is an all or nothing deal ... you either are or you aren't.
12 beers in 4 hours would probably put you over the BAC limit for drunk driving. The same would be true for 12 glasses of wine and 12 mixed drinks (assuming it was only 1 oz of booze per drink).
No matter how much the folks around the A want to save or change the A, the only one who can do it is the A him/herself. AA helps thoses who know they have a problem and want the change.
He doesn't think he has a problem
You might want to let SIL know about this site, so she knows she's not alone.
I wish you and your family peace.