Merging or fodder help

If your units need any of their skills, then fodder.

If some of these duplicates have bad IVs, it isn't a bad idea to merge them since they'll lose their bane but keep their boon.

If I were you, I would merge all my Fjorms because Fjorm comes as a bonus hero on Arena. So you could get higher arena scores on that season

Depends somewhat on IVs.

S.Lucina I tend to fodder because swift sparrow is good and 5* exclusive. Or even the egg could be interesting, especially now that mystic boost is a thing.

SF Nino I would probably fodder, but if you want some more bulk without fortify fliers then merging can be considered. But swift sparrow is good; aerobatics is tricky on a defense team, and even spd smoke can save feathers and grails.

S.Camilla definitely fodder. Juicy wave is good; hone fliers is borderline broken.

L.Azura I would fodder. Extra stats do very little on a dancer. Aerobatics I already discussed; B flier duel is maybe good if you already merged a blue flier (but I wouldn't go out of my way to do it; arena scoring is a joke). Atk tactic is even an option because Legault isn't easy to pull.

Fjorm has multiple fodder options including shield pulse and atk/def bond, which isn't as rare as it used to be especially when you have an extra flying Tiki. Or drive atk even, to save grails, but shield pulse is probably priority. But if you're big on arena you're probably best to merge.

Flying Tiki fodder for atk/def bond or merge. I'm not so convinced about atk/def bond these days. Enemy phase units who don't use spd probably want steady stance 4 or just go dual phase OHKO with spiral if they're infantry. If you have so much speed you don't need more, I don't see why you should play passive and enemy phase. But if you want to save some resources it's still decent.