Some time ago my hen Ellie suddenly became very lethargic and she had yellow poop. Blood work came back consistent with infection and/or inflammation. The vet treated her for both (antibiotic/antiinflammatory)even before the test results were back as she crashed fast and didn't look like she would live to wait for the results and happily she rallied beautifully and has been the picture of health since (that was more than a year and a half ago). I think she would have succumbed to whatever it was were it not for the meds. Your birds may have something completely different - and I'm so sorry for what's been happening - but I share the story because it's possible they may need meds.
JJ
JJ