Hi trunkman,
one thing that I have heard is that thin whites are a component of old eggs. Do you collect right away and then use in the order you collected? Just curious, because otherwise it could be something nutritional.
Thin shells with plenty of oyster shell around, could mean that your chickens aren't metabolizing the oyster shell. This is interesting because my brown layers have a bit thinner shells than my white layer. One way to boost absorption of the calcium is to be sure that the pH of their water is acidic enough. put 1 tablespoon of apple cider vinegar in their water and see if that doesn't help a bit. If your water is highly alkaline maybe even 2Tbsp of ACV per gallon. Another nutritional component hens need is plenty of vitamin D3. It is possible to get chicken vitamins at a supply store, like
Tractor supply, or on line. I purchased some for human consumption vitamin D3 and crushed a tablet mixed in with some feed I was giving my chickens when an egg shell seemed thin. I had noticed at the time that I had placed the movable coop in a very shady spot and with the holidays hadn't given them as much free-ranging time as usual so they could go sun bathe. (vitamin D-- the "sunshine vitamin")
So two things, ACV in their drinking water and be sure that their diet contains adequate vitamin D. With fewer hours of natural sunlight the chickens have less time to absorb the components to use vitamin D.
Hope this may help a little bit. Post back to us when you have the 'cure' and what it was that got your eggs to the way you want them. Oh and one other thing....if your brown egg layers produce eggs at a faster rate than your Easter Eggers, or if they are older, they may have less calcium. The slowly produced egg (every other day for example) versus the fast (daily) egg requires more calcium from the chicken.