Puppy diet

I would like everyones thoughts on a good diet for Possum. Currently she is being fed, chicken breast mince, a little brown rice, and puppy biscuits. Oggy & Flute are on a real fish thing at the moment. They have tuna one night, and sardines the other, with some dog biscuits.(biscuits=kibble) We try and vary their diet but they are just not as keen with other foods, they just prefer fish. Plus the vet thinks that Flute is alergic to chicken, so we have removed that from Oggy's & Flutes diet all together. I was thinking of feeding Possum fish also, but was wondering if this is a good thing to do. My premise being is that their meals will basically smell the same.
Also Flute used to have chicken wings which helped her teeth, but with chicken off the menu, and wanting to give her something that she can really chew on, without preservatives, I was at a bit of a loss. We were probably guilty of over feeding her with yummy snacks which were very high in preservatives. This I feel would not have helped her condition at all, so we are quite wary of what we feed her now. It was a process of elimanation that we narrowed the food problem down to chicken also.
Suggestions and advice appreciated:)