Garchomp
Give it a life orb instead of a mega stone, for 2 reasons.
1. Mega Gardevoir is better, and can also be more useful in double battles.
2. Mega Garchomp has Sand Force, but since no one in your team can summon a sandstorm, you aren't making use of this ability.
I suggest to go with rough skin.
Give Garchomp earthquake if you aren't going with mega Gardevoir, since she has Telepathy.
Gardevoir
Looks good, but if you want to use mega gardevoir, replace Moonblast with Hyper Voice.
Also, give her the life orb if you still want to use mega Garchomp.
Bisharp
Go with knock off, replace the dread plate with focus sash, replace iron defense with swords dance, EV train him so that he gets MAX speed and attack, and you should be good.
Talonflame
Gale Wings is way better than flame body.
If you give it Brave Bird, Flare Blitz, roost and Tailwind, you get priority setup, heal, and attack.
The best EV training is MAX speed and attack.
Snorlax
I think it's best to EV train him at HP/def/sp. def, then replace snore with power up punch so that you can raise attack, since you already have a lum berry to cure the sleep (Chesto berry is probably better, since you can get paralyzed/burned/poisoned/frozen and it will cure, wich will ruin your strategy).
You could also give him leftovers to heal every turn.
Empoleon
Give him leftovers, and replace water pulse with scald.
I think it's better to replace surf with something else, but i can't think of anything that would fit within this set.
Hope i helped!
Just ask me anything about the changes if you don't understand 'em.
