Charizard-Replace Wing Attack with Rock Slide, and go with Swords Dance or Belly Drum instead of Slash.
Flamethrower
Earthquake
Rock Slide
Swords Dance/Belly Drum
@Leftovers.
Lapras-Not bad, but Body Slam wouldn't be a bad replacement for either Confuse Ray or Psychic. Actually, you could be replace Confuse Ray and Psychic with the Sleep Talk/Rest combo, that works pretty good on Lapras.
Lapras
Surf
Ice Beam
Psychic/Sleep Talk(w/Rest)
Confuse Ray/Rest(w/Sleep Talk)
@Leftovers.
Tyranitar-Good, just go with Flamethrower over Toxic.
Heracross-Heracross also makes good use of the Sleep Talk/Rest combo.
Heracross
Earthquake
Megahorn
Sleep Talk
Rest
@Leftovers.
Dragonite has a great attack stat, so you will want to make sure that all of his moves are not Special Attacks, get at least one move in there that runs off of it's attack. Also, considering that Thunder only has 70% accuracy, Thunderbolt is a better choice IMO.
Dragonite
Ice Beam
Thunder Wave
Thunderbolt
Wing Attack/Double-Edge
@Leftovers.
Meganium-Don't worry about not having Earthquake for Meganium. Also, Sunny Day/Solarbeam is a little too dangerous to use IMO. Sunny Day powers up fire type attacks, which Meganium is already weak too.
Meganium
Razor Leaf
Leech Seed
Light Screen
Synthesis
@Leftovers.
Overall: Your team has a 3x weakness to Rock types (Charizard, Lapras, and Dragonite.)
And yes, I think that Leftovers would be the best attachment for all of your Pokémon.
If you want a Blissey/Miltank in your team, then Lapras would probably be the best choice in your team to replace. That way, you would be getting rid of the 3x Rock weakness too. If you replace Lapras, then go ahead and put Surf on Tyranitar instead of Flamethrower, so you will still have a Water type attack. Your Dragonite has Ice Beam, so your team would still have an Ice type attack. Anyways, here are some Blissey/Miltank movesets.
Blissey
Ice Beam
Light Screen
Heal Bell
Softboiled
@Leftovers.
Miltank
Body Slam
Curse
Heal Bell
Milk Drink
@Leftovers.