Alright, so a fourth generation in PSIII would be a little dull without Dark Force running around. Maybe an "epilogue" where you have to clean-up the last of Dark Force's followers or stop someone from starting another Orakian-Layan war would work. Whatever, just suppose there was a fourth generation.. which pairing would produce the best character?
Note: Adan-Gwyn are out for obvious reasons. Aron-Kara also since they're first cousins (their parents are brother & sister). Yeah, Ayn and Thea were second cousins (their parents were cousins) but that's generally considered acceptable (albeit a little weird).
I gotta go with Crys-Laya, a very strong fighter with a range of magic.