Advice for team

I have yet to complete the E4 on this game and I'm currently in Laverre City getting my 6th badge.
My team currently is:
Gardevoir : 48
Trace
Rash

• Confusion
• Magical Leaf
• Psychic
• Calm Mind

Jolteon: 44
Volt Absorb
Modest

• Double Kick
• Discharge
• Thunder Shock
• Quick Attack

Haxorus: 49
Mold Breaker
Adamant

• Dragon Claw
• Swords Dance
• Slash
• False Swipe

Charizard: 46
Blaze
Naive

• Slash
• Wing Attack
• Flame Burst
• Ember

I've been having random pokemon in my last two slots to get the exp for the evolution so I can get their Pokedex data, but I'm not sure who I want as my last two.

I spent a good portion of time going through the first part of the game to get all of the starters so I have:
Greninja, Chestnaught, Delphox, Lapras, Blastoise, Venusaur, Gengar, Diancie, Lucario, TalonFlame, Golem, Snorlax, Tyrantrum, Pawniard, Vibrava, Pikachu, Amaura, Gible and heracross(currently in party to simply be leveled up from 26)

I know the moveset's need work, but they are set for being able to simply do mass amounts of poke battles so there are a few weak attack moves, also my haxorus has false swipe to simply get catching pokemon a lot easier so I can just one hit 1 hp them then catch them.

I want to get all the pokemon in the pokedex so a pokemon meant explicitly for catching pokemon is a needed recommendation but also, any suggestions on the last two of my slots would be appreciated.

But overall, who should I add in to my last two slots for training :)

You're going to need a Water type so you have something to traverse the waters with. Which one you use is up to you, there's plenty of Water type Pokemon, plenty of good ones.

I don't remember when/where you get the TMs for them, but Earthquake and/or Poison Jab would be good on Haxorus. At this point in the game you have the HM for Fly, so teach that to Charizard (replace Wing Attack). Fly makes your life so much easier. Charizard also wants Flamethrower, which it'll learn upon it's next level-up. The other moves will depend on if you're mega evolving Charizard when you use it and which form it mega evolves into.