That sure is a cozy looking little home.
You are right though, they need a lot more room, and will be much happier in a 10 gallon tank when you get it.
It is safe for them to eat the calcium sand, but it is not a very safe substrate. The calcium sand will clump up when it gets wet, and can pack into a crab's shell, dry hard, and trap them in it. It also will grow mold and smell very bad when it stays wet.
A better sand would be Carib Sea brand Aragonite sand, with Oolitic grains. You can usually find it at pet stores that have supplies for salt water fish tanks. The grain size should be "Select" or "Sugar Grain" as those are the only grain sizes that are Oolitic. Oolitic means they are rounded grains, not sharp, and there is next to no risk of a sharp grain of sand getting into a crab's shell and puncturing it's abdomen or causing irritation.
If it is too pricey for you, or too hard to find, it might be best to switch to all Eco Earth. Expand the Eco Earth with your marine salt water to limit mold growth.
You MUST get a water conditioner that removes chloramines and neutralizes heavy metals. Tap water usually contains chlorine, which will blister your crab's gills, causing pain and damage.
It is often better to just purchase distilled water, which is ok because if you are using a marine salt mix, it replaces any electrolytes that were removed in distillation.
It is good that you changed their food, but it is important that they get some good protein sources as well as those fruits and veggies. They are not vegetarians, and need some meat and also things like wood and crunchy leaves! Seaweed is also very important. You can find seaweed at the pet store sold as algae. Don't buy fish food though, it often has Ethoxyquin preservative in it.
They need good calcium sources too. When your mom or dad are cooking dinner, ask for a bit of raw unseasoned meat, like half a teaspoon in size (they don't need much) and microwave it for about 15 seconds to cook it. Put that in their food dish, any kind of meat, including shrimp and fish! I like to buy a shrimp (one!) from the meat counter at my grocery store, steam it, then chop it up (shell, legs and all) and give my crabs a little and freeze the rest to put in their dish maybe about twice a week. Cork bark is cheap at the pet store, and they love to eat and climb on that, as well as cholla wood. Don't use any wooden half logs that are meant for reptiles, those are cedar and are not safe for your crabs.
As for one crab liking it cold and the other warm, this is exactly why it is important to offer them a good temperature range like you say you have. They do not regulate their own body temperature, and have to move about in their environment to do it. Offering a temperature range lets your crabs cool down when they need it, and warm up when they need it. We cannot know what they need, but they instinctively do. You will find a crab enjoys the cold for a while, then suddenly you find him basking in the heat of the lamp for days on end. If we offer them what they need, we know they are happier and healthier.
so i stoped feeding them that and now feed them fruits and veggies. Then for humidity I keep the humidity at always 70%-80%. The heat is kinda being hard because i have a light on the sand half of the tank because its kinda cold for them, but one will sit in front of the light but the other one like to be on the cold wet side? So why are they so diffrent because i would of thought that he would rather be warm then cold?
I got a question is it safe for my hermit crab to nibble at some of the calcium sand? And with the corner net they keep climbing up and then try to go upside down and will fall sometime, will that hurt them?