I have a strange hunch that if the show went on longer - we would have found that Trubel and Nick were step brother and step sister via his mom... Age wise she was approximately the right age to have been born after Nick's parents "died"....
Maybe there would even have been a twist that Trubel was Nick's full sister.. So for example Mom was pregnant when Dad was killed and she ran off and remarried or whatever... Then "they" caught back up with Mom and murdered the family again...