This is such a tricky one to handle. First make sure you check for eggs lots during the day and remove them soon as you can. Eating eggs can be through lack of food or vitamins, not so in this case, or lack of water, boredom, fun, habit. All it needs is one hen and soon they all start. I have tried blowing the eggs and filling with mustard, chilli, curry but they love it lol! You need to try and give them something they prefer to eggs!
If it was just one or two hens then I move them to quarantine to save the others watching and following the habit. Try re-organising the coup, move the nest boxes or provide a deeper hay nesting box bedding, give them lots of other toys and things to do.

Good luck,