Hi, gerbel.
I agree that you and your wife have to do whats necessary to protect the children.
Does your mil drink during the day, if that is when she is caring for the littles?
Even if she doesn't, she is likely not at her best because she is hungover.
Not a good scenario for the kids.
At the end of the day, this is your mil's choice.
Well, if she is addicted to alcohol, choice went out the window some time back.
What I am saying is, you can't control someone else's behavior, but you can control your response to it.
Good luck and good thoughts.