Years back, we had a thread very similar to yours. Baby chicks were dying and the OP had no clue. Neither did we. It was just as mysterious as your situation. The thread was left without an update for over a year.
The OP came back and finally updated. It turned out they had to move out of their house because the water was contaminated. It's been so long, I forget the details, but there was another similar thread just a couple years ago. The OP had a well, and the water was extremely high in iron. There's a thing about iron that binds with bacteria. It can kill baby chicks.
A necropsy would be a big help in understanding why your chicks are dying. Coccidia needs direct contact with the victim. It's not spread through the air. Water would be a common denominator in all your chicks, and could answer the question why brand new chicks that have never been on the ground are dying.