D. Hax has a fairly standard moveset. If you are going to run crunch or one of the fang moves for coverage, it might be worth picking up an ability capsule to give it strong jaw instead. If not maybe look at swapping either it and/or aqua tail for either aqua jet or bullet punch. With adamant and max atk ev’s, after a swords dance you can effectively sweep with your priority moves. Life orb or even a metronome would be effective on these builds.
D.Gard would probably benefit from livewire over nuzzle. If you are going to run 4 atk, you might as will give it an assault vest and make it a sp.def god. The wiki also says they gave it clear body as an alternative ability. Since you have Garchomp it might be worth swapping over as well.
Chandelure has too much redundancy in my opinion. Running livewire would give an effective way to have the majority of your opponents mons statused for the hex boost, meaning you wouldn’t need shadow ball or potentially will-o. You could drop hex and will-o for sub and calm mind. You could drop hex and pick up energy ball, also potentially pick up trick and run choice scarf/specs. You can also swap will-o for wildfire. Lot’s of options here.
Honestly, I think your best choices for a mega are in between D. Venusaur and D. Bisharp, but you should choose one and stick with it rather than alternate. Bisharp particularly should be built around technician if you choose it.
Venusaur should lose return. It has a bunch of great options to replace it. Calm mind, taunt, dual screens, sub, heal bell, hyper voice, magic coat, worry seed, and even trick room if you wanted to run some slower members. You should probably give this either your mega stone or leftovers.
If you run bisharp as your mega, try to get it jolly nature and dump everything into speed and atk. Replace blaze kick with power-up punch/mach punch/U-turn and swap drain punch for roost.
If you buy a hidden base you can gain access to the friend safari, which gives mons a 1/5 chance of having their hidden ability. This means you can catch a hidden ability gabite as long as you have 8 badges. See the wiki for a list of users names here: https://wiki.p-insurgence.com/Friend_Safari
I would probably run Garchomp as a defensive set since you really don’t have a defensive wall on your entire team. If you choose to, pump hp, def and spd and drop fire fang for fire blast and potentially dragon claw for dragon tail. Also give it a rocky helmet. You could also swap Garchomp out for D. Avalugg. It’s EQ isn’t going to be hitting anywhere near as hard, but it gives access to hazzard removal with rapid spin as well as slack off for recovery. It also has access to spikes as well as stealth rock.
It’s also worth mentioning that you can farm the hidden grotto in cortisol road part of the dream realm for dream mist, which is like an ability capsule that gives a mon it’s hidden ability.