Glad to meet you, New England neighbor. Do put your question in the Emergencies/Illness forum for a quicker and probably more complete answer. The folks here are just saying hello to new members.
I think it's pretty special that chickens chose you. Best wishes with those sick chickens. If you have one of the bodies of a chicken that died, you can send it to a
necropsy lab and they can tell you very exactly what killed the chicken. It can be a life saver (quite literally) for the rest of your birds.