Yeah your team needs so much work, as pretty much not a single one is close to being competitively viable.
D. Quagsire is a horrible choice against pretty much any opponent, so swap that out for something like thick fat ability D. Snorlax that knows earthquake, drain punch, seed bomb, belly drum/bulk up w/ an adamant nature.
D. Charizard is a special attacker, so there’s no point in teaching it physical moves. You want either timid or modest nature and have it know shadow ball, dragon pulse/draco meteor, sludge bomb, flamethrower
D. Haxorus should have jolly/adamant nature. If using water veil ability, then have it know swords dance, iron head, aqua jet, earthquake. If strong jaw then you can run iron head, crunch, ice fang, aqua tail. It should hold either expert belt, choice band, or focus sash
I highly recommend using d. scyther instead of d. scizor, as the speed difference and hustle ability is way more useful. should be jolly/adamant nature and know hone claws, close combat, icicle crash, night slash. have it hold focus sash. D. Charizard is a way better mega anyway, and you should only have one pokemon holding a mega stone at any time.
D. muk should only know physical attacking moves. Teach it Earthquake, drain punch, poison jab/gunk shot, fire punch/rock tomb. Ability is up to you and I’d recommend adamant nature, or could maybe go for a more defensive nature too w/ minimize
Again, normal Haxorus is a physical attacker, so any special moves are completely wasted. dragon claw, iron head, earthquake/low kick, dragon dance is better way to go. Jolly/adamant nature. You could run a mega stone with this if you really wanted, and if so give d. charizard choice specs instead of mega stone. I’d probably swap it out entirely since you already have a dragon type with d. charizard and a possible steel with d. haxorus. Probably should put in a timid D. Gardevoir/D. Chandelure in your team.