I play as a dual wielding warrior, but i'm not sure whether these two perks will affect me:

Fighting Stance: Power attacks with one handed weapons use 25% less stamina
Savage Strike: Standing power attacks do 25% more damage
Critical Strike: Can do one handed power attack while sprinting

Are these only of use if swinging a weapon in one hand or will they work if i'm dual wielding?

Seems like they all should work.
I'm not sure about the last one though because you can't relay move much with duel-wield power attacks.

Save game, get and test perk, load back if it doesn't work.

I don't know and I suggest you to try it yourself (save just after taking the perk). Sometimes people advice you with their best intention but without having tested themselves and you can end up realising you have taken a useless perk many hours later.