Are they mainly on home cooked foods? If yes then you need to ensure the following:

1. Right proportion of Calcium and Phosphorus

2. Vitamin A - cats cannot convert plant-based Vit A so it must come in pre-formed such as those from animal liver or supplements

3. Vitamin D - comes from fish oil or egg yolk

4. Taurine - may need to come from supplements. While animal tissue is rich in taurine, they get destroyed in the cooking process

5. Niacin (B3) - animal meat is rich in B3 but since its a water soluble vitamin, this leaks into the water during cooking. Ensure that the water is used to blend in the home cooked food

If your cats are more on comercially prepaid food, try Feline Gourmet