If you can not cull the birds, ISOLATE them immediately.
Keep them in a seperate pen and better yet building.
Give them starter and water with a small amount of oxytetracycline, go sparingly with this.
If they are not better in a few days, cull them. Have a friend do it if you can not.
Good luck. I have ONE polish hen in isolation and she is getting better, yet if she is not well in a few days, she has to go. I had a rather bad out break of some upper respiratory desease, about 10 of my birds got it, mostly the polish.
I fear that they are now all carriers and any bird I put in the flock will get this. I will let you know, because I am going to be forced to do this in a few weeks. The nursery birds are getting very big and I have 22 chicks waiting in the kitchen for the nursery.
The nursery is an enclosed portable with fans, heat lamps, oil/electrc heater and is sectioned off for the various type of birds I am raising. It is completely pedator proof and located near the house far from the chicken barn.
It is just not home without chicks in the kitchen.
I have an incubator full now too since the hens are laying steady and seem very happy.