You have a number of things that need to be corrected in order to have healthy crabs. See my replies below.
Be sure to read through the care sheets, they have all the information that you need:
http://www.hermitcrabassociation.com/ph ... .php?f=120
1. What kind of substrate is used in your tank and how deep is it?
I have coconut fiber even though I need to get all purpose sand too, I just couldn’t afford it after getting the coconut dirt. It’s 2 inches deep the biggest crab is a medium
Curly - Your substrate is not deep enough. It need to be at least 6 inches or three times as deep as your largest crab, whichever is deeper. It needs to be moist enough to hold it's shape (sand castle consistency) but not so wet that water pools.
2. Do you have gauges in the tank to measure temperature and humidity? If so, where are they located and what temperature and humidity do they usually read?
They’re high up where the crabs can’t reach them and the temperatures usually 70-80 and the humidity’s usually 50-90 and I mist the tank when it’s at 50
Curly - It would be good to see what the temp is at the level where the crabs are. Humidity of 50% is not high enough to allow crabs to breathe properly. You need to find a way to get the humidity more consistent, over 75%. Proper substrate can help. Is the lid sealed? Have you calibrated your hygrometer? Is it digital or analog?
3. Is a heat source used in the tank? If so, what?
I don’t use heat for the tank bc the thermometer usually shows that it’s higher than 69 and lower than 90
4. What types of water are available (fresh or salt) and how is the water treated (what brands of dechlorinator or salt mix and what ratio is used to mix it)?
I have fresh and saltwater separately and I use either tap water (there’s a filter on the water that takes out all chemicals), zephyrhills or purified bottled water. I put two teaspoons of “hermit crab salt water conditioner” in a 2 cup container to store.
Curly - You need to use a dechlorinator such as Prime, I would not trust the filter. Bottled water also needs to be treated. I don't believe that is a proper salt for hermit crabs, even though it is marketed as such. It needs to be a marine salt such as Instant Ocean.
5. What kinds of food do you feed and how often is it replaced?
I feed them food from hermit crab patch but until i have more I’m stuck with jurassidiet. I replace food/water every day.
6. How long have you had the crab and what species is it, if known?
I’ve had him about 1-3 years and it’s a purple pincher
7. Has your crab molted, and how long ago did it happen?
It did a surface molt a week and a half ago
Curly - Surface molting is a sign that something is very wrong, it is not normal for crabs to molt on the surface. Your crab is in a weakened state now, and needs to be kep isolated from the other crabs. Crabs go naked when they do not have enough energy to carry a shell. I am afraid to have to say, but your crab is in serious danger, which may be irreversable.
8. What type of housing are the crabs kept in, what size is it and what kind of lid is on the housing?
A 50 gal exo terrarium with a highly secured lid, 4 hideouts, one of them being a large cave, and climbing sticks
9. How many crabs are in the tank and about how large are they?
8: 6 mediums 2 smalls
10. How many extra shells are usually kept in the tank, if any?
I don’t keep track but I put at least more than 5
Curly - HCA recommends at least 3-5 extra shells per crab. That would be 24-40 extra shells. Check the care sheets for info about proper shells.
11. Have there been any fumes or chemicals near the crabitat recently?
No
12. How often do you clean the tank and how?
I clean the tank every few months by taking everything out and replacing the substrate
Curly - When you have proper substrate, you do not need to ever replace all of it.
13. Are sponges used in the water dish? If so, how are they cleaned?
No
14. Has anything new been added to your crabitat recently?
I got 2 small crabs yesterday
15. Is there any other information you would like to share that might be helpful (anything that is regularly part of your crab care, playtime, bathing, etc.)?
No
16. Please describe the emergency situation in detail.
He seems mostly fine now but the other days he was either running around naked or trying on shells
Curly - A naked crab will die. He needs to be re-shelled asap. You need more shells so he can find one he likes and that feels good to him. 
You have to use the dechlorinator for both freshwater and marine saltwater. Both pools should be deep enough for them to fully submerge in and safe enough for them to get out of. You can get instant ocean off of Amazon, or at most pet stores.