They look and act healthy but I’m pretty sure they’re not eating because the level in their food dish never goes down. 
Right now they’re ignoring Jurassic brand crab food. I’ve tried giving them (cooked) meat, lettuce and even a little peanut butter but they never eat it.
I’ve had them since early May and I’m getting worried. Any helpful hints? (I had pet crabs back in college and they would only eat peanut butter but at least they’d eat. And they would “sing” to me.)
I use the FMR brand Land Hermit Crab Food and the Treat (which smells good!). I think a lot of petstores use that brand. Mine eat pretty well. From what I’ve read, meat is bad for them. In the wild, hermit crabs eat fallen fruit. I’ve given mine fresh fruit, but they eat very little of it. Make sure to keep the aquarium really humid. Also, every once in a while, I mix sea salt into a small dish of water and put that in with them. They LOVE it. Petstores will actually sell you “salt water for pets”, but I just use enough sea salt to make the water taste salty, but not “ocean salty”.
There are some really good websites about hermies. I particularly like the ones that are written by people who keep lots of them as pets.
Good luck.