Please help me build the best team possible

[cfencl]

Hi my name is Chris. I want to build the best team possible with my favorite 6 pokemon. Can you help me?
 

1. Mega Venusaur= Buddy (male)
   
   1. Nature= Modest
      
   2. Item= Venusaurite
      
   3. Ability= Chlorophyll/Thick Fat
      
   4. Giga Drain
      
   5. Sludge Bomb
      
   6. Leech Seed
      
   7. Synthesis
      
2. Dragonite= Willie (female)
   
   1. Nature= Adamant
      
   2. Item= Flyinium Z
      
   3. Ability= Marvel Scale
      
   4. Outrage
      
   5. Fly
      
   6. Rock Slide
      
   7. Dragon Dance
      
3. Jolteon= Zen (male)
   
   1. Nature= Timid
      
   2. Item= Choice Specs
      
   3. Ability= Volt Absorb
      
   4. Thunderbolt
      
   5. Volt Switch
      
   6. Roar
      
   7. Protect
      
4. Gyarados= Sabre (male)
   
   1. Nature= Jolly
      
   2. Item= Life Orb?/Leftovers?
      
   3. Ability= Moxie
      
   4. Waterfall
      
   5. Earthquake
      
   6. Ice Fang
      
   7. Dragon Dance
      
5. Arcanine= Kaze (female)
   
   1. Nature= Adamant
      
   2. Item= Life Orb?/Leftovers?/Rocky Helmet?
      
   3. Ability= Intimidate
      
   4. Flare Blitz
      
   5. Extreme Speed
      
   6. Crunch/Protect/Close Combat
      
   7. Roar
      
6. Gengar= Punk (male)
   
   1. Nature= Timid
      
   2. Item= Life Orb?/Focus Sash?
      
   3. Ability= Cursed Body
      
   4. Shadow Ball
      
   5. Sludge Bomb
      
   6. Dazzling Gleam
      
   7. Focus Blast
      

 
I like double battles the most. I want to have a more clear strategy with using the team made of my favorite Pokémon. I am open to all suggestions to make the team better.  Any wisdom you can share?
 
I’m still working on my strategy. I’ve paired my pokemon into 3 teams. My first team is my Mega Venusaur with Dragonite. Venusaur could start but breaking down the opponent while Dragonite deals the major damage. My second team is Gyarados and Jolteon. Jolteon can protect Gyarados from electric attacks while Gyarados can deal with a variety of types. My third team is Gengar and Arcanine. They are mostly offensive so they would finish off whatever opponents are left. What are people’s thoughts?