This is my thought on the members i want to use.
*Ninetales (Timid) (Drought) (Heat Rock)
-Nasty Plot. Solar Beam. Flamethrower. Hypnosis.
*Rotom Heat (Calm) (Light Clay)
-Will-O-Wisp. Overheat. Thunderbolt. Light Screen.
*Talonflame (Adamant) (Gale Wings) (Life Orb)
-Tailwind. Brave Bird. Roost. Flare Blitz.
*Chandelure (Modest) (Infiltrator) (Choice Scarf)
-Trick. Shadow Ball. Fire Blast. Energy Ball.
*Volcarona (Calm) (Flame Body) (Leftovers)
-Quiver Dance. Bug Buzz. Roost. Heat Wave.
Apart from them i'm stuck between a Mega Charizard X or Mega Blaziken and/or set-ups for them.
The main problem with mono-Fire teams is that the vast majority of them are weak to Stealth Rock.
Since Ninetales is supposed to be the most important member of the team and the main priority is trying to maintain it to set up Drought again when needed, it's better off being defensive:
-Flamethrower
-Will-o-Wisp
-Rest
-Sleep Talk
Nature: Calm
EVs: 248 HP/120 SDef/136 Spe
Item: Heat Rock
Ability: Drought
Light Clay is only effective for Pokemon that use both Reflect and Light Screen, IMO. Your Heat Rotom set lacks reliable recovery, so drop it for Pain Split. Tl;dr:
-Volt Switch
-Overheat
-Will-o-Wisp
-Pain Split/Rest
Nature: Bold
EVs: 248 HP/252 Def/8 SDef
Item: Leftovers/Chesto Berry
However, Heatran is a better option for a defensive Fire Pokemon because of its Stealth Rock neutrality; however, you can still use Wash Rotom if you want for the Ground immunity:
-Stealth Rock
-Lava Plume
-Toxic
-Taunt/Protect/Roar
Nature: Calm
EVs: 248 HP/192 SDef/68 Spe
Item: Leftovers
Life Orb makes Talonflame worn down even faster in conjunction with its recoil-inducing STABs:
-Swords Dance
-Flare Blitz
-Brave Bird/Acrobatics
-Roost
Nature: Jolly
EVs: 252 Atk/4 Def/252 Spe
Item: Sharp Beak/Sky Plate/none
Ability: Gale Wings
or
-Flare Blitz
-Brave Bird
-U-turn
-Steel Wing/Tailwind
Nature: Jolly/Adamant
EVs: 252 Atk/4 Def/252 Spe
Item: Choice Band
Ability: Gale Wings
However, if you're playing Smogon monotype, Talonflame is banned. Arcanine or Infernape make decent substitutes, as both can help against Heatran, which you struggle with. Consider them for any other substitutions you might want to make:
Arcanine:
-Flare Blitz
-Extreme Speed
-Wild Charge
-Close Combat/Crunch
Nature: Jolly/Adamant
EVs: 252 Atk/4 SDef/252 Spe
Item: Life Orb
Ability: Intimidate/Flash Fire
Infernape:
-Fire Blast/Flare Blitz
-Close Combat
-Gunk Shot/
-Grass Knot/Hidden Power (Ice)/Thunder Punch
Nature: Naive
EVs: 100 HP/156 SAtk/252 Spe or 188 Atk/68 SAtk/252 Spe
Item: Life Orb
A Calm nature is a waste on Volcarona, since it has a decent Speed to use Quiver Dance with. Heat Wave is outclassed by Fire Blast in singles, as Fire Blast is stronger and still decently accurate:
-Quiver Dance
-Fire Blast/Hidden Power (Ground)
-Bug Buzz
-Giga Drain
Nature: Timid
EVs: 252 SAtk/4 SDef/252 Spe
Item: Passho Berry/Lum Berry
Ability: Flame Body
If you're playing Smogon monotype, (Mega) Blaziken is banned as well. However, if you're not, feel free to use it. It brings another Stealth Rock neutrality. It also helps against Heatran:
-Flare Blitz
-High Jump Kick
-Knock Off/Stone Edge/Protect
-Swords Dance/Protect
Nature: Adamant
EVs: 252 Atk/4 SDef/252 Spe
Item: Blazikenite
Ability: Speed Boost
If you want to use Charizard X, here are the sets to use. It makes for a neat physical attacker, and using Earthquake on it still helps against Heatran:
-Dragon Dance
-Flare Blitz
-Dragon Claw
-Roost
Nature: Jolly
EVs: 252 Atk/4 Def/252 Spe
Item: Charizardite X
Ability: Blaze
or
-Flare Blitz
-Dragon Claw/Earthquake
-Will-o-Wisp
-Roost
Nature: Impish
EVs: 248 HP/100 Def/160 Spe
Item: Charizardite X
Ability: Blaze
or
-Swords Dance
-Flare Blitz
-Dragon Claw/Outrage
-Tailwind/Roost
Nature: Adamant
EVs: 40 HP/252 Atk/216 Spe
Item: Charizardite X
Ability: Blaze
