I have a hen named Shiloh. She is an eggeater, herself. If any hen has layed an egg before her in the morning she will eat it before she lays hers. I have her some oyster shells then she stopped. Now if she doesn't have her oyster shells she will go rate back to eggeating.
Sometimes an egg will break in the nesting box. If any hen sees it she will eat it to clean up the nest. If your hens are laying weak shells were they are easily broken, the hens will start eating the eggs more. I say some oyster shells will help out your hens. You want to mix it up in their food, so they have to eat it. Some people have separate feeders for things like oyster shells, but I say you mix it up in their food first. Then maybe later you can have it separate if you want.
You could also give their own eggshells to eateat, but you have to prepare them in a way that they don't know that it eggshells because it could make it worse. Good luck with your hens.