Fishing
Two fathers and two sons were fishing at a lake. By noon everyone had caught a fish, so they walked home. When they returned, everyone was overjoyed that three fish were caught. No fish were lost, stolen, or thrown back. Everyone brought their fish all the way home. How can this be if the two fathers and two sons all caught fish?
There was a grandpa(father), a dad(father & son), and a son(son).