I don't see where the poster said Mom or Son was family. "There was a Mother and her son." She used pronouns like Mom/Son to make it clear who she was talking about. Second, the mother paid for two seats for herself (thank you!), and a third for her son. She should get all three seats. What was more likely was the jerk in the third seat liked not having an entire seat taken up next to him. There is a time I will not switch seats, but this certainly would not have been one of them.