I did not have any of the 3 possible proposed crabs, however upon inspecting my Journal of Pets I discovered my trusted Shore Crab H/P (Rare) had the same selection of moves available to it. Using the above provided TD Script, my Shore Crab was easily able to dispatch all three of this encounter's challengers and remain at optimal health, the other pets were able to sit the bench very comfortably. I'm leaving a comment as this dungeon is currently hot off the b.net client. Hope this info helps. Happy Petting! ;P
The third pet should have access to other abilities than elemental in case a cockroach sneaks into the backline. I see you have used shale hatchlings for later stages, a Blazehound or Blazing Cindercrawler would be nice. In another entry, someone's suggested a Teroclaw Hatchling aswell.