TWINS?!

I am getting married in October so naturally there has been tons of baby talk by our parents and siblings. We know we want kids and don’t want to wait too terribly long but I just found out that my fiancé has twins on his side of the family. His great grandpa was a twin and also had 2 other sets of twin siblings!! That’s 3 sets of twins from one set of parents. Nobody else in the family has had twins yet. Is there a chance he has the gene? It’s skipped 2 whole generations. It’s making me panic. Is it luck of the draw who has twins or is it a pretty strong possibility??