I think that it is important to step in, for your grandchildren’s sake. Has he ever had a drug addiction?
Meth is such an awful drug. From what I know about it, if you are addicted, you need professional help to get off of it.
It can make people extremely violent.
You really need to figure this out now. You need to protect those children, God forbid anything happen to them.
Best of Luck to you.