There is a huge amount of OU threats that can sweep your team. Mega Charizard X, Mega Mawile, Azumarill, Terrakion, Talonflame, Greninja and more can deal high amounts of damage to your team or just outright sweep it. I also see no way that you can touch the pink blobs known as Chansey and Blissey. Heatran and Mega Venusaur can pretty much do what it wants after Gardevoir goes down as well. Your team is also quite slow apart from Thundurus and Scolipede (which don't really revenge kill anyway), something I'll try to fix.
Espeon does not need a Lum Berry if it has Magic Bounce. The Magic Bounce ability will bounce back any status moves like Thunder Wave and Toxic, meaning that the Lum Berry will only help on the rare occasion a move's side effect of inflicting a status occurs. The Lum Berry is essentially useless for this reason, if you want to use that Espeon set use Leftovers instead. The set itself is flawed anyway, and Espeon is doing nothing for your team when you already have Gardevoir which is running an almost identical set. Replace it with something that can counter some of the previously mentioned Pokemon. A Pokemon with Fighting coverage would help against a number of them. I recommend using a physical attacker also, since you only have one. This leaves AV Conkeldurr and Breloom as good options (although they don't do any better than Espeon does against Charizard and Talonflame). You should also consoider a Defogger, since your team has a huge problem with Stealth Rock.
Leftovers is better than Rocky Helmet on Ferrothorn in my opinion, you already have Iron Barbs which works well enough. You should also use a more balanced EV spread since Ferrothorn is the only real wall on your team. 252 HP / 88 Def / 168 SpD is the generic spread that works nicely. I also question your use of both Power Whip and Gyro Ball; just stick with one of them. Usually I'd say Gyro Ball, but because there are so many Water types that threaten your team I'm going to recommend that you keep Power Whip and replace Gyro Ball with something like Thunder Wave that will support your team since it's so slow.
Gardevoir needs speed to move first, so put your HP EVs into Speed instead. Also consider Hidden Power Fire or Ground over Calm Mind, which will only come in handy occasionally. The former hits Bug/Steel types and Ferrothorn hard, and the latter surprises Heatran which is present on many teams.
Dragonite has no EVs and you didn't list its nature. Apart from that though, consider Earthquake over Fire Punch for Heatran and also Dragon Dance over Roost since you'll need speed to evade being revenge killed.
You don't really need a Baton Passer, especially not one that passes physical boosts since you only have one physical attacker on your team. I recommend you use Garchomp instead (specifically Scarfed Garchomp so you have a revenge killer). It can counter Charizard X even when it has +1 Speed, it can OHKO Terrakion and Mawile, deal good damage to Greninja and it scares Talonflame with Stone Edge.
If your heart is set on Scolipede, it NEEDS an attacking move. Taunt will shut you down and will allow your opponent to set up. Use an attacking move (eg. Megahorn) over Iron Defence, which isn't really doing much for you.
Use this Thundurus set over yours:
Thundurus @ Leftovers
Ability: Prankster
EVs: 4 Def / 252 SpA / 252 Spe
Timid Nature
- Nasty Plot
- Thunderbolt
- Hidden Power Ice / Thunder Wave
- Focus Blast
This set has better coverage than the one you use has, that's pretty much all there is to it. You should also consider using a defogger in Thundurus' place since your team has problems with Stealth Rock; Mandibuzz is one of the very best out there, and it will also give you another wall.
What I'd do if I were you. Hope this helped!
