What brand of cat food is best for overweight cats?

I have 2 cats. They are both overweight. We feed them Purina Naturals or something like that. We want the best, dry cat food designed specifically for overweight cats. They are adults, 5 and 9 years old. We feed them 1/3 of a cup twice a day, once in the morning, and once at night. We give them snacks throughout the day as well. I think we are feeding them too much. What do you think?•How much food do they need each day?•And how many times to they need to be fed that amount?