Hi I'm new this thread but unfortunately not to disease. The problem with respiratory diseases is that they can pretty much all look the same. Some have some distinguishing characteristics but even those won't be present in every case. If you can figure it out, you still have limited treatment options if you choose to go that route, without some veterinary help. You did the right thing by trying to get a definitive diagnosis. If will help you to know how to proceed, and answer some of your questions about its ability to spread to other species. I think the focus is on husbandry currently. Immediately separating those showing symptoms was smart. While you're waiting for a diagnosis just continue to observe, isolate/cull, take care not to spread contamination yourself in caring for the birds, provide clean water, good food and avoid stressing the birds (and yourself). Illness is always difficult but it doesn't last forever. Anybody who has kept chickens for more than three years has probably had to deal with it. I once had to depopulate the entire flock. You also tend to learn what works for your environment. I don't bring anything in after the end of this month until the weather warms up in March. For my set up I had to put in 1/2 inch poultry wire and cover the outdoor runs to keep wild birds out. I also believe that with some issues, you can successfully breed for resistance. Hang in and eventually you will have a vigorous healthy flock again.