Food for multiple cats of different ages

Question
Hi. I have 2 rescue cats, mother-daughter relation. The mother is 11 yr. at 7 lbs. and the daughter is 6 yr. at 14 lbs. Both cats are on a canned-food diet, with an occasional dry food treat. I am trying to find a dry food with substantial nutrients for both age groups, mostly for days I am unable to make it home to provide canned food and dry food is out for 24 hours. The food provided after leaving the shelter caused health problems with the mother (Purina ONE - Indoor + Hairball). I have since removed this food from their diet as of last week. The vet recommended giving both cats prescription food, but I didn't think that was necessary for the 6 yr. old who is doing fine. I am currently providing prescription food to the mother until i can find a suitable food which can be shared. Is it safe to provide a senior diet food such as "Hill's Science Diet Age Defying Senior Dry Cat Food" for both cats? If not, do you have a recommendation on dry cat food? Thank you! - Just another cat lover.

Answer
Yes, you can feed the senior food to the younger cat. It is a complete food.  The senior food has a little less protein, but more vitamins and minerals.  It also has reduced phosphorus and will maintain an alkaline urine pH to prevent struvite stones.