Thank you for the link, but I don't think they send stuff to Australia.
I talked to my Vet about what was going and he told me to try the calcium tablets. When he last checked them over he said they were very healthy. I talked to him about their total dislike of oyster shell and he said they were fine and showed no signs of calcium problems. This problem has only happened since they started to lay. He also said that they might be laying these weird eggs because their reproductive systems are still getting the hang of it. Also I do feed them a lot of dark greens and I often see them in the veggie patch nibbling on parsley and coriander, which they seem to like and also they love the grass (they have so much of that to peck at each day).
I still keep a dish of oyster shell in their coop, just in case they want to give it a try again.
I try to give them a variety of food as well as their layer pellets and layer scratch.
They are spoiled chickens, but all my animals are.