Alright, I'm going to rate this thing.
Where is the Ninetales? Ninetales really helps, as it basically weakens your Water weakness, as well as powering up STAB moves. Right now, the most expendable Pokemon on your team seems to be Arcanine. Replace Arcanine for this Ninetales:
Ninetales (M) @ Leftovers

Trait: Drought
EVs: 252 HP / 124 Def / 132 Spd
Timid Nature (+Spd, -Atk)
- Flamethrower
- Will-O-Wisp
- Roar
- Substitute
Now, onto your other Pokemon:
For your Volcarona, you seem to be running defensive, to take full advantage of Flame Body. However, since we Sun now, having Sun boosted Volcarona is absolutely deadly. So change your EVs to 4 Def / 252 SAtk / 252 Spd, and swap your Roost for Hidden Power [Rock] to allow you to hit Rotom-H and Heatran.
Infernape could really use a mixed set here. You have 3 Choice Users, which isn't all that great, in my opinion. Try the Life Orb Infernape:
Infernape (M) @ Life Orb

Trait: Iron Fist
EVs: 252 Atk / 4 SAtk / 252 Spd
Naive Nature (+Spd, -SDef)
- Overheat
- Mach Punch
- Close Combat
- ThunderPunch
Heatran can fill in as a Specially Defensive Pokemon, as you do need something to sponge strong Special moves, and Heatran has great bulk for it.
Heatran (F) @ Leftovers

Trait: Flash Fire
EVs: 248 HP / 248 SDef / 12 Spd
Calm Nature (+SDef, -Atk)
- Lava Plume
- Stealth Rock
- Earth Power
- Hidden Power [Ice]
Darmanitan can use Rock Slide instead of Earthquake for more damage due to Sheer Force.
Your Rotom-H needs a complete revamp when using Choice Specs, as you do need some Speed on your Special side right now:
Rotom-H @ Choice Specs

Trait: Levitate
EVs: 252 SAtk / 4 SDef / 252 Spd
Timid Nature (+Spd, -Atk)
- Overheat
- Volt Switch
- Hidden Power [Grass]
- Trick