I've fed my cats separately at different times in their lives, for different reasons. This might work for you, except for the cat that's not food motivated, because that cat won't eat right away, leaving the food for the others to finish.
Not sure if I'm reading this right, does he give each cat 1 cup of dry food a day???
Not sure if I'm reading this right, does he give each cat 1 cup of dry food a day???