Yes, don't cause a panic, but check with your County Extension office to see if they do necroscopies. My state does them at the Univ. of Florida, but I'd have to ship the chicken there. I did them myself when my chickens died, sent digital pics to the vet there for a diagnosis. Since yours are all named and are "pets", you likely won't be able to stomach this, so you need to find someone who can. Don't mention "mass deaths" until you get results back.
Do you think there is any possibility that it is "foul play"? Irritated neighbors feeding them something poisonous?
What about well-meaning but stupid kids feeding them something poisonous?
Good luck, and I hope you don't lose any more.

Do you think there is any possibility that it is "foul play"? Irritated neighbors feeding them something poisonous?
What about well-meaning but stupid kids feeding them something poisonous?
Good luck, and I hope you don't lose any more.