I would get some of your level 20 Pokémon to level 35 because Skyla's Pokémon range to level 30. Try and fight Audinos because they shed off a lot of Exp Points. And a quick question, it doesn't look like you have any electric or rock types for Skyla's birds. Does your Pignite have rollout? If not, I would recommend you get a megnezone, just level up magneton 1 level in Chargestone Cave. I'm not forcing you to do it, it's just a suggestion.
I hope this helped!