Three Pokemon holding the sme item isn't a problem if this is for battles on Pokemon Showdown or with your friends. If its for official tournaments or Battle Spot battles, then its a problem.
But it's actually Forretress that needs the Leftovers the most, since it lacks any sort of recovery whatsoever. Vaporeon can heal itself with Wish+Protect (or even Water Absorb), and Gourgeist has Leech Seed and Pain Split for recovery. So give Vaporeon or Gourgeist a Lum Berry to deal with status. The other one could use...maybe a Sitrus Berry or an Enigma Berry. Not a lotta options.
And does Tailwind really work on a Choice set?
Talonflame uses Tailwind as a last-ditch effort to support the team before it goes down. Speaking of Talonflame, it needs enough Speed EVs to outspeed Jolly Mega Kangaskhan (Adamant with 92 HP/252 Atk/164 Spe).
Dragonite needs Fire Punch or Thunder Punch over Earthquake or Roost.
Also, since Talonflame and Dragonite are weak to Stealth Rock, a Rapid Spinner is needed. Excadrill and Starmie do this job for you:
Excadrill:
-Earthquake
-Rock Slide
-Rapid Spin
-Shadow Claw/Swords Dance
Nature: Adamant/Jolly
EVs: 252 Atk/4 Def/252 Spe
Item: Life Orb/Assault Vest/Air Balloon
Ability: Mold Breaker/Sand Rush
Starmie:
-Hydro Pump/Surf
-Psyshock/Thunderbolt
-Ice Beam
-Rapid Spin
Nature: Timid
EVs: 252 SAtk/4 SDef/252 Spe
Item: Life Orb/Leftovers
Ability: Natural Cure
or
-Scald
-Rapid Spin
-Psyshock/Ice Beam/Thunderbolt
-Recover
Nature: Timid
EVs: 248 HP/32 Def/4 SAtk/224 Spe
Item: Leftovers
Ability: Natural Cure