Hermit crabs have maggots in their shells what do I do?

[Cierra Nugent]

My mother bought hermit crabs from a wholesale place (I know bad idea) and when they arrived one hermit crab was covered in maggots and missing an entire leg so we took it home thinking it was dead. We later found out it was alive so we gave it multiple baths in dechlorinated water until no more maggots came off and kept him isolated for about a week then put him in with the rest. Except now others keep dying. Today we found one dead and when we picked him up he fell out of the shell and was covered in maggots (he had been dead for less than a day). The tank has proper conditions and fresh food and water and we sterilize everything that goes in their tank. So what can I do to help them? I don't want anymore of them to die.
(We also bought 5 jumbo crabs but they seem perfectly healthy aside from one missing a part of its pincer)