4 crabs out of shells

Question
my daughter has 4 hermit crabs.  basically 2 small and 2 XL.  wed p.m. she read on line that they can be given a bath by putting them on their "back" in a bowl of treated water.  when they right themselves (immediately) take them out & put them in a bowl with papertowls to dry & then back into the tank.  they all righted themselves in about 5 seconds.  thurs a.m. i found 3 of them coming out of their shells with the fourth following by dinner time.  1 xl was moving all around without his shell, one was lethargic. 1 small removed himself from his shell while in a saltwater dish.  for light/heat source we have a heat lamp.  for a habitat we have sand on one half of the tank and small pebble/rocks on the other.  this was recommended by the pet store.  the rocks & sand are about 2 inches thick.  the sand is thinner in some areas due to it being dragged around.  i turned their sunlamp off during the day as a website said the light can be stressful, but i wrapped the tank sides with a towel to maintain heat.  they have 2 freshwater bowls & one saltwater bowl.  FRI AM:  the XL "mover" is on his back, with all legs missing.  XL "lethargic" is also on back but has changed locations a few times, Small "saltwater" is on its back & so is the other.  All of them are still showing varying degrees of movement, however, none seem to be going into any shells.  the 2 XLs are 2 wks into our tank & they came looking like they needed new shells so we provided 2 new choices for them.  I'm a bit surprised that all left their shells at the same time & that they are taking so long to get into their new shells.  What should we be doing?  Did we do something wrong?   HELP!  do we have much time left???  thank you

Answer
For all of the crabs in the tank to react at the same time we almost always look to some sort of environmental factor. You say the bath water was "treated". I'm assuming that you mean dechlorinated but is there anything else it was treated with? What was the temperature of the water?

Has anyone sprayed hairspray, cleaning products, or bug killers in the room?

What was the humidity/temperature in the tank. Light will not stress your crab, think of them in the wild, they are exposed to the sun. However they do need places to hide if they prefer shade.