My ex-mil lied to cover up her son's drug problems, make false inflammatory statements about me in an effort to gain custody of my children, assisted in the kidnapping of my oldest child by her son.
I was granted sole custody, allowed to leave the state with my children. Ex got supervised visitation in the state I live in. My ex and his mother have not seen or spoken to the kids in nearly 11 years. Things could have been entirely different, but it's a choice she made and has been living with the consequences for over a decade.
Some grandparents forget that they are NOT their grandchild's parent. The sooner they acknowledge that fact and act accordingly, the better the relationship will be with their grandchildren.