cat foods?

I have some real questions about cat foods and how to get my cats on a diet that helps with allergies. I switched the cats to Blue Buffalo Sensitive Skin and my allergy cat has adjusted just fine to it but the kitten who is healthy - she's sick. She is still active and bright eyed but her stools are just soo loose. Force feeding her pet pectin is causing us some real stress (and minor injuries).  Torti's can be such bitches!  So I have tried to put her back on Avoderm and that's just a miserable fiasco trying to keep the cats from eating each other's food.

Cosmo's ears are starting to get dirty again and his acne appears gone but just barely. Maybe the blue buffalo is not the best choice but I just don't know what to do! Thank God the dog is so much easier. She eats the Avoderm and her coat is just fab.  I could kick myself for not putting her on that sooner.