Lets see...
Slurpuff, perfectly fine
Whimsicott, could use leftovers instead of focus sash with a moveset like that
Scrafty, may I suggest dragon dance for a larger coverage and an extra sweeper
Volcarona, I would put the remaining evs in spa
Gyarados, a good moveset would be:
Gyarados @ life orb
Ability: Intimidate
EVs: 252 Atk / 252 Spe/ 4hp
Adamant Nature
- Waterfall
- Dragon Dance
- Earthquake
- Stone edge
I use this set and it works very well
I would replace roserade for mega-venasuar as your team lacks a bulky pokemon:
Venusaur @ Venusaurite
Ability: Chlorophyll
EVs: 252 HP / 240 Def / 16 Spe
Bold Nature
- Giga Drain
- Sludge Bomb
- Synthesis
- Hidden Power Fire