Volcaronas: overheat silver wind will o wisp flamethrower
Tyranitar: gigs impact dragon tail crunch earthquake
Terrakion: healing hand retaliate rock slide scared sword
Garchomp: dragon rush dig surf shadow claw
And amoongoss and Aggon aren't high enough level
Volcarona is better off setting up Quiver Dances then smashing things. It's also too physically defensively weak for support:
-Quiver Dance
-Fiery Dance/Fire Blast
-Bug Buzz
-Hidden Power (Rock/Ground)/Giga Drain
Nature: Timid
EVs: 252 SAtk/4 SDef/252 Spe
Item: Life Orb
or
-Quiver Dance
-Bug Buzz
-Fire Blast/Fiery Dance
-Roost
Nature: Timid
EVs: 252 HP/240 Def/16 Spe
Item: Leftovers
or
-Quiver Dance
-Bug Buzz
-Fire Blast/Fiery Dance
-Rest
Nature: Modest
EVs: 160 HP/236 SAtk/112 Spe
Item: Chesto Berry
Tyranitar has a wide movepool to take advantage of. Never use Hyper Beam-style moves competitively; they leave you a sitting duck the next turn:
-Stealth Rock
-Crunch
-Pursuit
-Fire Blast/Stone Edge/Superpower
Nature: Sassy/Careful
EVs: 252 HP/4 Atk/252 SDef
Item: Leftovers
Ability: Sand Stream
or
-Crunch
-Pursuit
-Stone Edge
-Superpower
Nature: Adamant/Jolly
EVs: 180 HP/252 Atk/76 Spe (Adamant) or 4 HP/252 Atk/252 Spe (Jolly)
Item: Choice Band (Adamant)/Choice Scarf (Jolly)
Ability: Sand Stream
Terrakion needs some serious redoing. It has stronger STABs in Close Combat and Stone Edge:
-Rock Polish
-Swords Dance
-Close Combat
-Stone Edge
Nature: Jolly/Adamant
EVs: 4 HP/252 Atk/252 Spe
Item: Life Orb/Air Balloon/Rock Gem
or
-Close Combat
-Stone Edge
-X-Scissor
-Quick Attack/Sacred Sword/Rock Slide
Nature: Jolly
EVs: 4 HP/252 Atk/252 Spe
Item: Choice Band/Choice Scarf
or
-Stealth Rock
-Taunt/Swords Dance
-Stone Edge
-Close Combat
Nature: Jolly
EVs: 252 Atk/4 SDef/252 Spe
Item: Focus Sash
or
-Substitute
-Swords Dance
-Close Combat
-Stone Edge
Nature: Jolly
EVs: 4 HP/252 Atk/252 Spe
Item: Rock Gem/Life Orb/Salac Berry
Garchomp learns Earthquake. Use it:
-Outrage
-Earthquake
-Fire Fang/Aqua Tail
-Dragon Claw/Dual Chop
Nature: Jolly
EVs: 4 HP/252 Atk/252 Spe
Item: Choice Band/Choice Scarf
or
-Swords Dance
-Earthquake
-Outrage
-Fire Fang/Aqua Tail
Nature: Jolly
EVs: 4 HP/252 Atk/252 Spe
Item: Haban Berry/Yache Berry/Lum Berry
or
-Substitute
-Swords Dance
-Outrage
-Earthquake
Nature: Jolly
EVs: 4 HP/252 Atk/252 Spe
Item: Leftovers/Salac Berry
or
-Stealth Rock
-Outrage/Dragon Claw
-Earthquake
-Fire Blast/Swords Dance
Nature: Naive/Jolly
EVs: 4 HP/252 Atk/252 Spe
Item: Life Orb/Focus Sash
or
-Stealth Rock
-Dragon Claw/Dragon Tail
-Earthquake
-Fire Blast/Aqua Tail/Protect
Nature: Jolly
EVs: 252 HP/196 Def/60 Spe
Item: Leftovers
Looking at this team, you're vulnerable to bulky Waters. Ferrothorn fills in both Amoonguss' and Aggron's roles in one slot:
-Stealth Rock/Spikes
-Leech Seed
-Power Whip
-Gyro Ball/Thunder Wave/Protect
Nature: Relaxed
EVs: 252 HP/88 Def/168 SDef
Item: Leftovers/Shed Shell