I’m at the end of the Update so far. I have time to adjust things in my party. Here’s my preferred team:
Gallade
Lv.81
Nature: Relaxed
Item: Leftovers
Moves: Dazzling Gleam, Close Combat, Drain punch, Psychic
Milotic
Lv. 78
Nature: Timid
Item: Focus Band
Moves: Dragon Pulse, Recover, Hydro Pump, Moonblast (Planning to get rid of dragon pulse later with ice beam when it’s available)
Delta Charizard
Lv. 75
Nature: Lax
Item: Delta Charizardite
Moves: Shadow Ball, Lunar Cannon, Dragon Rush, Phantom Force
Charizard
Lv. 75
Nature: Bold
Item: Leftovers
Moves: Fly, Focus Blast, Flamethrower, Blast Burn
Thunderus
Lv. 75
Nature: Jolly
Item: Magnet
Moves: Dark Pulse, Discharge, Thunder, Agility (Most likely making it forget agility because it’s speed is already 190…)
Lilligant
Lv. 75
Nature: Brave
Item: Miracle Seed
Moves: Sleep Powder, Giga Drain, Energy Ball, Leaf Storm.
Anything I can improve on?
So obviosly the natures aren`t ideal, you could try breeding for better ones. If you don´t want to swap out any Pokemon, this is what I would go for.
Gallade is a physical attacker, so you shouldn´t run psychic and dazzling gleam on it. Try using some heart scales to get Psycho Cut and either Leaf Blade or Night Slash.
Milotic should be fine like this for a playthrough.
Mega Delta Charizard is a special attacker, so Dragon Pulse is better and also more accurate then Dragon Rush. And using 2 moves of the same type without any significant difference (priority for example) is redundant. Personally I also don´t like Lunar Cannon, since Shadow Ball is stronger in New Moon and hits everything supereffektively that Lunar Cannon would. It also has more PP. The best set right now is probably Shadow Ball, Dragon Pulse, Frost Breath and Confuse Ray/Shadow Sneak ( For priority)
Charizard learns Air Slash by move relearner, which would be better then fly, but not by much, so you could keep Fly for utility. Blast Burn is annoying because of the Recharge, you should get Roost, once it is available.
Since Thundurus Ability is Prankster you should run some status moves on it, especially livewire, it´s just too good not to use. Since you don´t have a ground type, Thunderbolt is a better option than Discharge (That way you don´t damage your other Pokemon in Double Battles).
Again having two moves of the same type isn´t useful on this Pokemon either and Thunder is really inaccurate. You should definitely run Thunderbolt and Livewire, Dark Pulse or Psychic are fine and Nasty Plot is really useful. Choose 2 of the 3.
You don´t have many options with Lilligant, but you definitely need Quiver Dance on this thing. Probably instead of Leaf Storm.
I hope I helped you out 
Thanks for the advice! Although I probably won’t change my delta charizard’s moveset, since I like a little diversity. And although inaccurate, dragon rush would be better because its attack is actually its second highest stat (I know, doesn’t make sense). Anything else, I definitely would try and make adjustments. Thanks again!