One of them is possibly Lin's dad :} or at least I hope so. It would be really annoying if it was anyone else Zuko is there just for the hell of it, I don't really believe it could be him xD even though it would be sooooo cool. Same for Sokka, unfortunately And for those who have no idea who Ohev is, he is a character from the comics only, who was a love interest for Toph.
Well, now that Su is confirmed as Toph's other daughter, I think Lin's father is Satoru or Ohev, and Su's is either Satoru or Sokka. Why Satoru so much? Because of The Rift. It's showing he's the father of one of them.