They are not being spiteful or doing it on purpose. You have to decide if it is a flock problem or an individual hen problem, or in your case, two hens. Chickens need a certain amount of calcium for their egg shells. They can get this from various sources, Layer feed, calcium supplements like oyster shell, some from certain plants they eat, or hard-shelled bugs or crustaceans, though it is hard for them to get enough just from plants or creepy crawlies. It’s not how much calcium is in one bite or from one source. It’s how much total calcium they eat in a day, and that averages over several days.
A possible source is form the rocks they use for grit, but that is only if that rock contains calcium. Limestone does but granite and a lot of other rocks do not. Just because they are eating rocks does not mean they are getting calcium. It has to be the right rocks.
Some hens do not have the instinct to seek out calcium if they need it for the eggs. The vast majority do but they are living animals. They are not all the same. Also, some hens are just not set up right inside to properly digest the calcium they eat. None of them digest all the calcium they eat, a lot goes right on through and out the back end, but some are really poor at digesting calcium. Still the odds of you having two of these are pretty bad. I doubt this is your problem.
Were the other five egg shells sufficiently hard and thick? If they are, there is enough calcium around for all of them to get it. If the other egg shells are thin then you should offer a calcium supplement, it’s a flock problem.
What it really sounds like to me is that you don’t have hens you have pullets just coming into lay. The hen’s internal egg making factory is fairly complicated. Most pullets get it right the first time but often there are glitches when a pullet first starts to lay. You can get huge double yolked eggs, tiny eggs with no yolk or maybe no white, misshapen eggs or strangely colored eggs, eggs with extremely thick shells or eggs with very thin or even no shell, just a membrane. Usually it doesn’t take them long to get the glitches out of their system but some can last a week or more.
Something else that makes me think you have pullets just coming into lay is the eggs dropped anywhere instead of in the nest. Again most pullets get it right to start with, but some seem to not know what is happening and just drop their first few eggs wherever they happen to be. That could be from the roosts at night or just walking around the coop or run. Once they gain control of the process they will start laying in a nest, either one you have for them or they’ll find a regular place to lay, maybe in a corner on the coop floor or maybe outside somewhere. But in the meantime you can find some in strange places.
Often when you are there looking at them I can be hard to know what is really going on, let alone across the internet. All I can do is guess what might be going on. I could be right or I could be way off.
Good luck!