Pelipper, Kingdra, and Swampert sets are okay.
Replace Tapu Koko's Nature's Madness and Grass Knot with Dazzling Gleam and maybe Hidden Power Ice. Nature's Madness can't kill and Hidden Power Ice covers more. Zap Plate is fine, but I suggest Choice Specs.
Choice Band Araquanid is only really good if you have Trick Room support, which you don't. I recommend Kabutops, but other Pokémon can also do the job. Here is a good set:
Kabutops @ Rockium-Z
Ability: Swift Swim
EVs: 252 Atk, 252 Spe, 4 HP
Adamant Nature
-Swords Dance
-Waterfall
-Stone Edge
-Aqua Jet
Steel types have lots of helpful resistances, so having one on your team could be good.
Ferrothorn @ Leftovers
Ability: Iron Barbs
EVs: 252 HP, 252 Def, 4 SpD
Impish Nature
-Stealth Rock
-Leech Seed
-Power Whip
-Knock Off
Ferrothorn has many resistances, including grass and electric, which hit water for super effective damage. Fire, which is a scary 4x weakness, is weakened by rain.
If you decide to keep Tapu Bulu, Horn Leech is a must. It hits hard and regains more HP than Leech Seed probably will. Replace Brick Break with Superpower, Bulk Up Wood Hamer and Megahorn with Stone Edge. Leftovers is a great item choice, but Assault Vest is a good option if you have all attacking moves, as it raises its low special defense stat. If you really want a setup move, Swords Dance completely outclasses Bulk Up.
Hope I helped! :)
