Personally, I wouldn't feed them pellets intended for rats. To be honest, I don't even feed mine pellets intended for crabs. Many of us feed an all natural diet.
That said, I wouldn't be concerned about your crabs eating or not. It's a common mistake that people make. Grapes are a good example of something I'm willing to bet your crabs have munched on without you noticing. They are very plump and crabs eat very little. So any of the flesh they have taken out could easily be missed.
Also, crabs can go months underground without food. So don't worry too much.
Your crabs are still well within the destressing period. Just give them time.
And if you're desperate to see them eat, I have a couple suggestions. Fresh cooked shrimp is a big hit in my tank. Leave the tail on and they'll even munch on that.
Fresh coconut is always gobbled up. and then there's the big one... The BIGGEST hit in my tank BY FAR is to cook a chicken drumstick without seasoning, remove a great deal of meat to expose the bone (but leave a little meat on) and then crack the bone in a few places to expose the marrow. My crabs LOVE bone marrow.
Your crabs are still well within the destressing period. Just give them time.