Complex sentence: His son is actor and former UCLA quarterback Mark Harmon, who is married to actress Pam Dawber, and he is the grandfather of actress Tracy Nelson and twins Matthew Nelson and Gunnar Nelson, who perform as the rock and country music act Nelson.
Split into simpler sentences: His son is actor and former UCLA quarterback Mark Harmon, who is married to actress Pam Dawber. Tom Harmon's grandchildren include actress Tracy Nelson and twins Matthew Nelson and Gunnar Nelson, who perform as the rock and country music act Nelson.