Your team has promise, but you might want to change shaymin from specs to life orb with synthesis. Running a set like this:
252sp atk/252spd/4 hp
Leftovers could be used if you want to live longer. A more defensive spread could also be used.
As far as replacing ninjask, milotic might work as a check to gligar and sabelye. There are a ton of sets, but the best for your situation would be:
Crocune could also be used, but he doesn't get a def boost when he's affected by status. There are also some weird blastoise sets like this, but avoid those. I hope it helped!