Red Claw crabs and fiddler crabs should only be kept in tanks with mostly land and a little bit of water. The water should also be brackish water as that is where they originate from. Usually anything that's labelled FW
'anything' generally isn't FW
(with some exceptions), they're usually BW to full marine.
Crabs always eat the leftover shell after they molt because the calcium in it helps their new shell harden faster, the female didn't move much because their natural instinct when molting is to hide in their shoreside burrows until their shells harden then returning to the mud flats to feed.
Any type of crab shouldn't be kept in full FW
or water without land, they'll eventually either try escaping the tank to reach higher ground or they'll die from being in the water for too long. Some people have kept them in tanks without land, but not for long periods of time (in excess of a few months).
Also, a 5g tank is too small for two red claws and a betta. The red claws will probably wind up killing each other as the males are pretty abusive to the females.