Hi members of HCA. I'm new to crab proper crab owning. I've checked the guides and set up a 10 gallon with 6 inches of 1/2 playland 1/2 EE, a heat mat on the side of the tank. I also have 15 different sized shells. Honestly have been lurking since October while I made sure everything was good. I still have many questions, though.

I have two crabs that I just got on Thursday, a small one in a green turbo who I have named Spencer and a medium named King's Arms who is in a brown and white snail shell and has buried under deep. He is in the corner that I designated to be the most pit. Spencer likes to go over there too. Should I be worried that Spencer is always digging in the same spot where my medium crab is buried? If King's Arms is molting, will Spencer possibly eat him even though he(Spencer) is smaller?
I have provided salt water( instant ocean mixed with bottled water that was purified by RO- I just ordered some Prime so I am waiting on that.) And freshwater. In the food bowl currently is apple, shrimp, eggshells, orange pepper, cherries, and chia seeds. I saw my small crab carry away some eggshell this morning.