8 week old chicks missing feathers

[bgreely]

I have 3, 8 week old, Dom chicks. 2 pullets and 1 cock. The 2 pullets are missing a large amount of feathers on their rear-ends, on their backs, and under their wings. The three of them are separated from my other 30 hens. I have also noticed that the three of them have the stinkiest poo I have ever smelled! I'm thinking something like cocci or intestinal so I started Corid this past Saturday. Would you all think I am on the right track? Maybe lice too? They are all eating and drinking normal too. Any suggestions or help would be greatly appreciated!