You said your daughter was 20. Is that even legal drinking age where you are from?
OK...this is just my opinion so please, take it for what it's worth.
It sounds to me like you're more afraid of losing your daughter again than you are of taking steps to actually help her.
Also, if they don't work, then where are they getting the alcohol????
You can't drag them to get help. The only help you can give them is the boundaries that were mentioned above and actually STICKING to them. I am a bit of a hard a$$ so my boundaries may seem a little shocking to you at this point.
They have been with you for less than a month and they have turned your home upside down and inside out. I can't even imagine what your other poor child must be feeling right now or your husband.
Mom, I know you love your daughter and obviously are willing to put up with a LOT to have her back but I'm sorry, boyfriend needs to go back to Cali number one. He is nothing more than a drinking buddy and he needs to find his OWN way. He isn't your responsibility and if your daughter follows him? Guess what, it's her choice.
He should be behind bars anyway for putting his hands on her.
Number two, they need to understand that if they want to play house, then they need to be mature enough to get one of their own.
"She can't live without him" I believe you said in your first post. It seems to me as if the only reason she can't live without him is because they appear to feed off of each others behaviors. If he's not around, who's she gonna get drunk with?
It's obvious that she has been surrounded by a disfunctional lifestyle most of her life and her problems go a lot deeper than the alcohol. She's not only addicted to alcohol, she's addicted to this guy and the relationship too, which is only going to get worse, the longer they continue the way they act.
I'm sure this is definitely not what you thought this reunion would be and my heart goes out to you. Unfortunately, this is however the situation at hand and it's time for a sobor round table meeting, complete with those boundaries and the penalties of what the violations will be. Your husband seems very supportive and he needs to be at your side, showing that united front, instead of just playing referee. Of course you need to express how much you love your daughter but love and guilt over hurting her feelings is not going to make her stop drinking or get rid of the boyfriend. All it will do is make you, your husband and your other child miserable.
I think you also need to ask your 10 year old how all of this is making her feel. 10 year olds are pretty smart and I'm sure this is definitely taking it's toll on her as well.
All in all, you really have to be willing to deal with the consequences that they may face from violating the boundaries and I hate to say it but just from what you've said, they are gonna going to break them.
If the first time they cross that line, you don't take the bull by the horns and enforce the rules, you are back at one.
I wish you all the strength in the world and I'll say a prayer for you.