“Family Fundamentals” is the filmmaker’s personal attempt to answer an explosive question: “What happens when conservative Christian families have gay children?” Armed with a digital camera, Dong takes the audience into the private and public lives of three families, where parents actively campaign against gay rights, despite having gay children themselves. Seemingly a search for common ground between two diametrically opposed groups, “Family Fundamentals” is also a report from the deep and unsettling culture war over homosexuality in America.