Oh holy Hannah Laryngotracheitis!!!! If you had that they would be shaking their heads and you would be seeing blood head level in your coop because they cannot clear their sinus/throat without shaking their heads. It is not treatable and culling as far as I know if the only thing to help them. Any other birds need to be inoculated against it from this point on, its deadly. If you don't see blood...possibly not.
When you said in the corner hunched up, this sounds like Coccidiosis and is treatable with Sulmet, Corid or what ever. Its best to treat and save them, especially where the next batch of birds you receive will do the same thing. Please get a milk product into them, this is not a cure, but its doing something.