Agreed; the 3 reincarnations have an entire game already. They have no reason to be in Fates other than popularity. They're all worse than their original incarnations too.
I'd remove them entirely.
I also agree with this. His base class is myrmidon, he's obsessed with swords, there's not a chance in hell he wouldn't fight for Hoshido. Morally, I think he'd be the least accepting of Nohr of the 3.
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If I were to change it, I would have 6 awakening children participate: Noire, Brady, Kjelle, Owain, Inigo, Severa.
(a quick explanation of those excluded: Morgan is too tied to Robin, Lucina is too important to the plot of Awakening, Yarne and Nah suck have unique classes that don't exist in Fates-land, Cynthia is very similar to Hinako (gameplay-wise), and Gerome is... Gerome. He's kind of similar to Percy too.)
Owain, Noire, and Brady would be in Hoshido. Noire can easily replace Setsuna, Owain can replace Hinata, Brady can replace Hayato (the story for that can be retconned- he just ended up with the Wind Tribe somehow).
Kjelle, Inigo and Severa would be in Nohr. Kjelle easily replaces Effie, who is basically the same character anyway.
I think that would be a pretty good balance, and it's a lot less haphazard than how the real Fates turned out.
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I made a document on my PC called "Hypothetical Fates Redesign) with exactly this listed in it.