What to do with my feathers

Well, I can't really choose for you.Your team seems pretty good to me. If you want to continue with these 4, Robin is a good pick for an upgrade

5 Star Robin to deal with the current meta(s) Takumi(s) Healers and other colorless followed by Roy to deal with the current uprising of Hectors. Fae is good but she doesn't gain much stats when upgraded and all her skills can be unlocked at 4 star.Peri only seems to be anti mage and can't really withstand other physical attackers.Sheena has the second best overall stats for axe wielders at 180 buuuut her lack of mobility would probably cause you the game (It would still work for story/event missions since they do give you time for preparation to enter the danger zones.)