Sarah, here is a list of quality low-fat foods that the DFA recommends: /best-dog-foods/suggested-low-fat-dog-food/
Why does it need to be low- to medium-protein again? If you are really set on it though, you may find this list helpful: /best-dog-foods/low-protein-dog-foods/
Also, you could well feed any dog food, even puppy food if it fits the phosphorus requirements, you just need to adjust the amount based on the dogs’ activity level and lifestyle. This calculator may be a good tool to consider: /dog-feeding-tips/dog-food-calculator/
So, you can try to match a food that is in both lists (the low-fat and the low-protein ones), and see if the phosphorus is right for your dogs. Then you can look up the kcal/cup of that food and see how much to feed less active dogs using the calculator.
Hope this helps!
