I'd suggest finding some wild Audino and grinding - your team, judging by their status as not being fully evolved, is far too underleveled to fight Skyla. Her team ranges from 40-42, and most of your team that evolves will have reached their final stage by 36(I'm looking at you: Dewott, Drilbur, and Darumaka).
Evolving Drilbur(at level 31) will be very helpful for you, as Excadrill's secondary Steel-typing has a very helpful resist against Skyla's flying moves, as well as the Psychic moves that half of her team carries. That leaves only Skarmory and Swanna as potential problems for Excadrill, which your Darumaka(which should be a Darmanitan at level 35) and Dewott(Samurott at 36) should be able to handle with ease.
While your Lucario is also of the Steel-type, his Fighting-typing as well makes Flying moves neutral, so he won't be too much of a help. You should also have Surf(given to you by Cheren), so I'd slap it on Dewott(if you haven't already) and go to Mistralton Cave and pick up Rock Slide. You'll also need Strength, which you should already have as well(as per the story), but a large number of your team is able to learn it, or you can just find a nice HM Slave. The majority of your team can learn Rock Slide, which will be very beneficial when fighting Skyla(sans Skarmory).
