Cool team you've got there, Ewgross! I think you've got a pretty decent Doubles setup here, as the mons themselves are strong choices, but I do have a few suggestions regarding the sets if you don't mind.
Mega Metagross:- Zen Headbutt is a powerful STAB move that does complement Iron Head, but the accuracy means you'll eventually miss at a crucial moment, putting your streak in jeopardy. For this reason I'd scrap it in favour of Thunder Punch, since opposing Gyarados could potentially cause problems. Protect's obviously a great move, but I also wouldn't rule out Bullet Punch as an emergency response to faster threats; it's decently powerful thanks to Tough Claws, but may require some trial and error as to which move would suit your team better.
Hitmontop:- Stone Miss is an awful move for the Maison, especially coming off Hitmontop's average Attack stat and not being STAB. Between Metagross and Intimidate-shuffling, Flying types shouldn't be a huge issue, and crits are beyond your control anyway. Hitmontop has great utility options for Doubles, so for the last slot I'd highly recommend Helping Hand; priority is what makes the move so reliable, and all 3 of your teammates can benefit from it. One more thing, what does a Careful nature do for you exactly with that EV spread? Sitrus Berry is a fine choice, but I think you'd be better served by Adamant to boost Close Combat's power.
Hydreigon:- Modest Life Orb is commonly seen in Triples play with Tailwind support (which you don't have), so I reckon a Choice Scarf would offer greater synergy with your team; with your existing EV spread it'll hit 225 Speed, outspeeding Accelgor4 & Darmanitan4 while tieing with Pinsir4. Draco Meteor's 130 Base Power is appealing, but again, the imperfect accuracy is less than ideal. I'd suggest swapping it for Dragon Pulse, Earth Power's good, then either Flamethrower or Surf in the last slot.
Gyarados:- Choice Scarf is certainly an interesting choice, but imo it's not too flash. A Dragon Dance set with Lum Berry might be the way to go, patching up Gyarados's mediocre Speed while simultaneously boosting its already impressive Attack. Waterfall for mandatory STAB, coverage-wise I'd actually suggest Earthquake; as far as I'm aware Wide Guard also protects against spread moves coming from your side of the field, meaning you can EQ/Surf without fear of damaging Hitmontop. Ice Fang sucks (to put it bluntly), Iron Head's pretty redundant since you've got MegaGross for Fairies, meaning you've got a free slot for Protect/Substitute. Return isn't a bad option either as Water/Normal coverage is pretty nice. I don't know what the optimal EV spread is for Adamant DD, but I'm sure you could find out on the first page somewhere. Best of luck!
Mega Metagross:- Zen Headbutt is a powerful STAB move that does complement Iron Head, but the accuracy means you'll eventually miss at a crucial moment, putting your streak in jeopardy. For this reason I'd scrap it in favour of Thunder Punch, since opposing Gyarados could potentially cause problems. Protect's obviously a great move, but I also wouldn't rule out Bullet Punch as an emergency response to faster threats; it's decently powerful thanks to Tough Claws, but may require some trial and error as to which move would suit your team better.
Hitmontop:- Stone Miss is an awful move for the Maison, especially coming off Hitmontop's average Attack stat and not being STAB. Between Metagross and Intimidate-shuffling, Flying types shouldn't be a huge issue, and crits are beyond your control anyway. Hitmontop has great utility options for Doubles, so for the last slot I'd highly recommend Helping Hand; priority is what makes the move so reliable, and all 3 of your teammates can benefit from it. One more thing, what does a Careful nature do for you exactly with that EV spread? Sitrus Berry is a fine choice, but I think you'd be better served by Adamant to boost Close Combat's power.
Hydreigon:- Modest Life Orb is commonly seen in Triples play with Tailwind support (which you don't have), so I reckon a Choice Scarf would offer greater synergy with your team; with your existing EV spread it'll hit 225 Speed, outspeeding Accelgor4 & Darmanitan4 while tieing with Pinsir4. Draco Meteor's 130 Base Power is appealing, but again, the imperfect accuracy is less than ideal. I'd suggest swapping it for Dragon Pulse, Earth Power's good, then either Flamethrower or Surf in the last slot.
Gyarados:- Choice Scarf is certainly an interesting choice, but imo it's not too flash. A Dragon Dance set with Lum Berry might be the way to go, patching up Gyarados's mediocre Speed while simultaneously boosting its already impressive Attack. Waterfall for mandatory STAB, coverage-wise I'd actually suggest Earthquake; as far as I'm aware Wide Guard also protects against spread moves coming from your side of the field, meaning you can EQ/Surf without fear of damaging Hitmontop. Ice Fang sucks (to put it bluntly), Iron Head's pretty redundant since you've got MegaGross for Fairies, meaning you've got a free slot for Protect/Substitute. Return isn't a bad option either as Water/Normal coverage is pretty nice. I don't know what the optimal EV spread is for Adamant DD, but I'm sure you could find out on the first page somewhere. Best of luck!