What are grandparents rights in Indiana?

My Father in law has recently threatened to sue us for visitation rights of our children. My husband and I have one together and he has 2 from a previous marriage. Although, my father in law is pretty unstable, we have never denied him opportunity to see the children, but he chose to take a trucking job for a year and whenever he was here, we didn't have my step sons. So he quit his job and calls us up demanding to see them on our weekend. We told him we were busy and told him we would plan on the next time we have them. He threatened it then, then came on the day we agreed to see them.. Then threatened again because we could only visit for an hour and a half. He tells us his girlfriend did this to her daughter and won, but her daughter was refusing and had them out of wedlock.