Who i should invest?

Well, Minerva can work with an attack bane considering Hone Fliers buff...

Camilla can appreciate the speed boon, but it takes away from her resistance...

Honestly, I'd have to go with Camilla, and that's mainly because she has better merge potential, but go with the unit you like the most.

As for the build, I'd probably just go for something basic, to be honest. Her refined Camilla's Axe grants a Goad effect to her and to certain allies, so you can combine her Axe with a Goad Fliers for even more support. Fury and Desperation and maybe a speed +3 seal.

There are other skills, of course, so this is just one way to build her.

I would invest I neither because Camilla is well know for being a Reinhardt counter and lowering her Res with DC will have a major issues
And she will just about tank some blue mages. I would go with +Spd/-Hp as this works better with out harming her Def or her Res and then she can abuse ploy skills like: Def or Atk Ploy. Her refine is only good in a flier emblem so investing Dew in her is probably not worth it.
A -Atk Minerva is the worst possible iv to have, but the LnD will increase her Atk. But likewise her Refine is Crazy, a Woa Do axe is amazing to have pair that with moonbow and you got a Green Nephenee.

I would wait untill you get better Ivs, their ivs aren't the best, if you desperately want to then the option is yours, not mine.

Camilla will leave you with more options - change her IVs if you want; max-merge if you want; her buffing ability to fliers is insane so she can easily find a role for her there; +spd basically gives her 34/39 offensive stats with prf before A-skill; specializes in any direction due to her balanced stats and prf effect to cover having slightly lower offensive IVs.

How to build her is dependent entirely on her teammates. The only piece that isn't likely to change is goad fliers.

There's fury, brazens, bond skills, even DC (then use Iote's shield seal); she can use drag back, hit and run, desperation, QR (with DC, to compete with mages who hit 50-ish spd or even Karla if she doesn't get OHKO'd, block their double and double back. Karla isn't bulky), flier formation, renewal, list goes on.

She'll take pretty much any special except glimmer/astra (moonbow or luna is likely better), but bonfire, ignis, aether, moonbow, even galeforce (with heavy blade seal, or tank a bit then finish charging it while in desperation. The latter is not for GC or chain modes without healer, though).

It's your role to decide how your team comes together. We can only give you ideas.