Rainbow Dash - Remove the cap rate, maybe give a slight conch-like speedboost to nearby players instead. Increase hp to 200. You'd need a base weapon as soda popper if you want to modify the popper for infinite flight.
Vinyl - Please, no extra knockback. That was pure cancer already, the knockback should've been halved. Have it mark targets for death if they get bounced high enough into the air.
Twilight - Think about it, 450 instant headshot. Any player who is good at sniper will abuse the crap out of that and destroy everything.
Fluttershy - Sounds fine, she was never strong before in the first place.
AJ - Any sentry that spawns at lvl 3 will be easy as HELL to just walk up to spawn with your team's support and just place a lvl 3 instantly. Then run away. Because if it's instant lvl 3s, no one would care to keep it healed, they'd just run away, get ammo, and build another when that one goes down. AJ was always broken, don't break it even more.
Chrys - Sounds fine.
That's my opinions and feedback on that. Hope you consider those for balancing if you do get that far.