Was Mark Peter's son?
Peter was married, and tradition says that his wife was martyred in Peter's presence, and, if I remember correctly, Peter did have a [biological] son. I can't remember Peter's son's name, but I'm quite sure that Mark was not Peter's biological son. Mark was the daughter of a certain Mary (Acts 12:12), but that wasn't Peter's wife. Maybe someone who knows this better than me can give some more information.
-A8