My daughter and son-in-law were a few years sober. They have been having hard times financially in the last couple of months.  He lost his job as a result of taking prescribed pain pills for a swollen ankle.  He doctor shopped and became addicted quickly.  They both avoided this as if it wasn't happening.  They cashed in his pension and went on a bender last night at a casino with the new found money.  My grandchildren are here with us for the weekend (as they are most weekends).  They are 11 & 14, son-in-law is step dad.  We get a phone call last night from him that our daughter has been missing for 3 hrs.  We could tell right away that he was high/drunk.  He's freaking out that she went out to the car 3 hours ago and never came back.  My husband tells him to call the police, and/or security, son-in-law is crying, yelling, slurring, etc.  He hangs up and calls security.  To make a long story short SIL couldn't even remember where the car was.  Security assists him in finding the car and low and behold my daughter is "passed out" in the car.  All the while we are here, 3 hours away getting ready to drive to where they are to help find her.  It was very scary and even as I'm typing this I can't believe how crazy it sounds.  Daughter denies she was drinking although we know she was just by her slurring words when we finally spoke to her last night.  She called this morning, denied any using/drinking and asked if we are still cooking out later today.  

I am not good at handling these things.  My main priority is to protect my grandchildren.  My daughter is an excellent mom when she is sober and loves her children very much. She has been an alcoholic and bulimic for many years.  She is 36 years old.  SIL is 52.  I am not a fan of his for many reasons.  The two of them met in AA.  

Please give me some advice as to how to handle this situation.  Thank you.