So sorry!
It's not going to go away, true, and it's best to actually get a diagnosis, so you can have a plan going forward. Your state veterinary college path lab can run tests, look them up.
No birds or equipment from this flock should go anywhere, and no new birds should come in, until all these birds are dead, and more time passes after that.
Wear 'coop clothes' and 'coop boots and shoes' that stay there, and don't leave your property. Obviously your birds have something contagious, if they are all sick, and many things can also affect your parrot.
Layer feed is meant for hens actively laying eggs, and nobody else. Change to an all flock feed with 20% protein, and fewer treats, with oyster shell in another dish, and grit also in a third dish.
Mary