You obviously have something serious going on. On the surface it is likely respiratory but there could be multiple maladies affecting them.
There is no treatment until you know the nature of the malady. Most people don't have a poultry vet nearby or even an avian vet. But what you do have is a state poultry diagnostic lab. Sometimes it is a state agency but usually the state university. In what state are you located?
In most cases you can contact them and they will send you a prepaid Fed=Ex label so you can ship a recently deceased bird for a necropsy. This is the only way to know how to proceed.
If we know your state, I can give you the contact information. If the lab is nearby, you can take a sick bird and they will humanely euthanize it and do the testing.
Refrigerate a dead until you can get it packaged and shipped. Don't freeze it.
