Need advice on weather or not to cull.

[MyCoop]

I have chickens of various ages. Basically a mail flock, and 8 week old grow out flock and a brooder full of chicks. It's appearent I have something contagious going on. It started with the brooder chicks not doing well some dying a few gasping and squeaking. No coughing or sneezing but puffy eyes. Main flock more and more are getting a swollen eye. 8 week old flock seemed good untill I heard one gurguling and it died I 2 days. Then a hen started gurguling and now won't come out from under coop. I know she is on eggs but not sure if she won't come out because she is sick or if she is broody or both.

Now another of the 8 week old flock looks sick. Lethargic, not eating and drinking a lot. I'm don't know what it is but it's spreading. Shouldd I cull the whole flock. Is there hope for the 8 week olds?