I think Toni was older than Erica. As to the romance, there was actually supposed to be a romance between Jed and Toni (yeah, I know, Dirty Dancing, shut up) but it was cut, according to the trivia section. Also, when you are fighting in a war, you aren't exactly interested in beep There was also the crush Erica had on Capt. Andy, remember? And maybe in the end, when the two survivors make it to freedom, Erica and Danny, they could've ended up getting married later on.

Could have been cousins, I think Ben Johnson simply referred to them as granddaughters.