Merge or Send Home?

I'd merge oboro and f corrin. Keep kagero handy in case you want to give her weapon away, same goes for roderick. Camilla has decent fodder with savage blow and brave axe, jagen has fort cav obviously and clair only has hit & run which really only works on melee flying units.

I wouldn't send any home. Expand your barracks. The feathers you get aren't worth it.

Most of them have excellent skills for skill inheritance at 4 Star rarity, so merging duplicates altogether is a bad idea to begin with.

Oboro has terrible set of skills for skill inheritance and can safely be sent home. But if you like her for whatever reason, then keep her and merge if you like.

Kagero is one of the few that can definitely benefit being a super-high merged unit since she doesn't really offer anything for skill inheritance either. Kagero does something Oboro cannot, so she's good to have even though she's not quite as hype nowadays.

You might want to hold onto some of them for Skill Inheritance. The notable ones are as follows:
1. Jagen- Fortify Cavalry
2. Roderick- Dragback & Firesweep Lance
3. F.Corrin- Hone Attack, Draconic Aura
4. Camilla- Savage Blow, Draconic Aura
5. Kagero- Poison Dagger (and Daggerbreaker... if that ever becomes meta)

Oboro and Claire don't really have anything worthwhile unless you like Seal Defense from Oboro.

Even Oboro can be useful for rally def fodder. Yeah rallies arent that great but can come in handy for certain challenges or squad assault. Then switch back to reposition or another movement skill when you are done.