That's a valid concern.Thank you for the welcome! The first papery shelled egg I found didn't cause too much concern. However, the count is up to 6 now. All but one was split open. I want to prevent them from tasting it and developing a bad habit of a taste for their own eggs.
Have you seen the pullets eating the oyster shell? I would toss it out with a handful of meal worms.
You can also feed a treat of yogurt with crushed human calcium with vitamin D in it to the girls for a week and see if that hardens up their shells. For 5 pullets I'd crush 2 tablets and mix it into about a 1/4 cup yogurt and feed each girl some of it.