Warning: Don't let him come!!!
It's obvious there is something wrong wity your father in law. If you have young children, they can become child molestion victims, no matter they are boys or girls. Your wife should learn about this field and she should be the one refusing to let her father come. My own grandfather fondled me and my brother when I was about 9 nine years old and I still feel hurt psychologically until today. He's an animal. Believe me, this is a true story. Please don't let this tragedy happen to your daughter or son!