Ninetails @ Leftovers
EVs: 252 HP, 120 Def, 136 Speed
Not much to say here; weather lead is a weather lead.
Victini @ Choice Band
Ability: Victory Star
EVs: 252 Atk, 4 Def, 252 Speed
Zen Headbutt/ Brick Break
Standard set for physical Victini; I would go for Zen Headbutt over Brick Break though, if only for STAB and flinch chance, but you can go for Brick Break if you want to bust through Reflect and Light Screen.
Kingdra @ Lum Berry/ Life Orb
Ability: Swift Swim
EVs: 236 Speed, 136 Atk, 136 Sp. Atk
I would go for Ice Beam over HP electric, in favour of a higher base power; Ice Beam has wider coverage. Also, Waterfall as an option from Surf, because since you're using Dragon Dance any way, might as well take advantage of Kingdra's boosted Attack.
Life Orb is an option; I think it might be better than Lum Berry because when you send Kingdra out, it's there to sweep and its chances of coming back are slim. Also, I guess even if Kingdra is either Toxic'd or Spored, you got Blissey to deal with that.
Venusaur @ Life Orb
EVs: 252 SpAtk, 252 Speed, 4 Sp. def
Sleep Powder/ Sludge Bomb
Max EVs in Speed, because then you're sure of outspeeding scarfed Pokemon like Mienshao or Zoroark in order to make full abuse of Sleep Powder/ Growth.
Sludge Bomb as an option because there are only 2 attacking moves in this set, and one of them is HP. Imo when a set needs to resort to HP for coverage, you're scraping the bottom of the barrel, trying to find something in the Pokemon's movepool.
Foretress @ Leftovers
EVs: 252 HP, 252 Def, 4 SpD
I would actually go for Spikes over Toxic Spikes; if your opponent should have a Poison type, especially Tentacruel on a rain team, then it'll absorb the Toxic Spikes and have no damage done. Spikes are there to do damage to Poison types too.
Blissey @ Leftovers
Ability: Natural Cure
EVs: 252 Def, 252 SpD, 4 HP
°Thunder Wave/ Toxic
°Flamethrower/ Ice Beam
On Blissey, I changed the EVs around; invest in Defence instead, since it's so rubbish you might as well give her max EVs there to allow some chance of survival when hit by a non-super effective physical move. Aromatherapy over Stealth Rock; you already have Forretress to deal with that, and some team support is always welcome. Thunder Wave or Toxic; you can use Toxic in order to stall out special sweepers.
You can consider an elemental move like Flamthrower or Ice Beam, since while Seismic Toss will do more damage, Ghost types are immune. Nothing really is immune to Ice Beam/ Flamethrower (bar Flash Fire Pokemon), so at least you'll do some damage all round.