W hen it comes to sappy holiday movies, you either scorn them as you would another pair of reindeer-themed socks, or you eagerly binge on offerings such as “My Southern Family Christmas,” produced by Hallmark and described thusly: “Under the guise of a journalist, Campbell has a chance to get to know her biological father for the first time — without him ever knowing who she really is. … Campbell must decide if she’s going to keep her identity a secret or reveal the truth to her father — a decision that will change their family Christmas forever.”