Sorry that you have sick birds and have lost one.
It would be a very good idea to refrigerate the body and have your State Lab test. The results from the lab will give you information that you can use to move forward in know how to manage and treat symptoms.
Let us know what the results say when you get them back.
As for what to do about the current sick bird(s), you've been given good suggestions from several posters on this thread. At this point I don't believe I can add to what has already been mentioned.