Mal: No idea who his father was. Mom raised him alone on the ranch... well, her'n 40 ranch hands.
Sarah: Her dad remarried after her mother left them to become an actress. He doesn't seem to make much time for her, though we see everything through her eyes, so it's not entirely accurate.
Martha: Clive clearly loves her even if he has his own problems. He's also very brave, doing what he can to save her when the Master's people are holding him and Francine hostage, and then fighting against the Master while they're on the Valiant.