Since your going to be evolving all of these Pokémon I recommend these EV investments:
Squirtle:
252 Defence, 252 HP, 4 Special Defence- Defensive
Gastly:
252 Special Attack, 252 Speed, 4 HP- Special Sweeper
Rotom:
252 Special Attack, 252 Speed, 4 HP- Special Sweeper or you could give it a bit more bulk
Froakie:
252 Special Attack, 252 Speed, 4 HP- Special Sweeper
I based these EV's on your Natures. Pokémon such as Greninja I would have actually given a Hasty or Naive Nature so It wouldn't receive a decrease in it's Attack Stat and it could use U-turn effectively but since yours has Modest I've just went with a completely different set.
Hope I helped :)