It my prove a challenge to stop. They have learned that the eggs are really good, and you will be in a race to collect the egg before it gets eaten. I have at least one Delaware that likes her eggs, but DH checks eggs 4-6 times a day and wins the egg race most days. I have also hung dark T-shirt material over the nest openings to make it dark in the nest.
I haven't tried booby trapped eggs, but if needed I would blow one of their eggs and fill it w/ Stadium mustard (I have several bottles in the pantry), seal the end w/ wax or nail polish and return it to the nest. I would not put other things in the egg shell that might sicken the chicken.
You may be faced with the task of culling the hens, not easy because if you give them away, the new owner needs to know what problems is being brought into her coop. I read where one poster after an entire season of egg eating, had her girls all molt last fall and quit laying. She reports this spring they appear to have forgotten that eggs are yummy and she is getting eggs again.
If I were in your shoes, I would cull, as in kill, the hens and start over. I am attached to my girls but they aren't 'pets'. If yours are pets then your choices may be limited.
Hopefully you get better suggestions for the others.