Thanks for the additional info, here’s a suggestion for an updated team. I don’t want to recommend anyone that scores less than what you currently have, so I’m sticking with Yen’Fay as my recommendation. To replace Caeda in this case.
Other A skills that work for Yen’Fay are Atk/Spd Solo 4 or a Stance skills. I made it so that Nino and Yen’Fay have the same Atk/Spd total. Both will benefit from Seteth’s gap skill if you build them like this. It works incredibly well with Atk/Spd Unity.
I’m aware Yen’Fay has a solo condition, meaning you have to place him one space away from other teammates to get all the effects, personally I have no problem with that.
I see no reason not to stick with Nino, especially seeing how much you invested in her
Iris’s Tome +Eff isn’t ideal when you can get her Atk buff from another source. I prefer +Atk or +Spd refine. Her best B skills are Null Follow-Up or Lull Spd/Res. Blade Session is currently the best skill for nukers.
It’s too bad you don’t have a Rouse 4 skill, but you don’t need a tier 4 for scoring. A tier 3 version can also work just fine. Just try to get visible buffs on ALL of Nino’s stats, either with her own C skill or by supporting her with a gap. Atk/Res Menace is also a pretty good option. If Nino doesn’t need her own C slot for getting all the visible buffs, you can go with something like Time’s Pulse or a Joint Drive.
Lastly, if you can get your hands on Ruptured Sky, it’s way superior to Aether which takes forever to charge.
As for the third unit, as long as you don’t have a legendary unit you can stick with Seteth. The build below uses B Duel flying for extra scoring, but you could also wait and see what Shigure’s refine has to offer. Thea is also coming up soon. Maybe don’t invest too much into Seteth right now if you plan to replace him sometime. I think Distant Counter is better replaced by the Duel or Sturdy Impact though.
While Y!Innes is a great FTP unit I enjoy using myself, he scores less than Caeda without C Duel Inf 4. Yen’Fay scores 2 points higher and it’s good to have someone on your team that’s build for enemy phasing some opponents. Something your previous team was lacking I think. Seteth is now a melee specialist and Nino will hit harder.
Btw since you have Far Save you can also build W!Ignatz instead of Seteth. B skill is flexible: Special Fighter and Slick Fighter are good options, the best one would be Savvy though. Weapon can also be Spendthrift bow.
I hope this helps