I want to call the cops on my grandpa-in-law
What made you want to call the cops on  him?
He bigamist and is disgustingly sleazy
Is he doing something to break the law? I think that if something dangerous is going on, you should call the cops, even if that person is part of your family.
He's a sick person and I'm calling the cops now.
You should do that if you feel you need to. I hope the cops can help your situation.