This actually would be a really shocking twist. I mean, Melia's race is super long lived and depending on how it goes a Blade Eater's physiology can grant them eternal youth. They could be Melia and Nia's respective daughters or they could also be attempts at the two to try and "recreate" Shulk and Rex.
Either way (or completely different) it'll be fun to figure out what their stories are.
Fiora I can understand. There's no reason to believe she'd want to share Shulk. But Pyra and Mythra seem like they'd be ok with Nia joining their harem.
