I am not sure if this is going to be helpful advice for you as you have more kitties than me, but I changed the amount of times I feed my cats per day, to leave longer times between meals and I dont leave any dry food for snacks.
So my two cats share 1/2 cup of dry food in the morning. They finish this with the speed of light.
They get 3oz of wet to share at around 3pm. They are usually so hungry by 3pm that they clear whatever it is that is given.
And 3oz at midnight. Again by midnight they follow me and meow at me to make sure I dont forget to feed them. This gets cleared really quickly as well.
I recently had to switch to cheap foods, but still had some wellness laying around (beef and chicken). They hate that flavor, but with how hungry they are, the plate was cleared.
I hope I dont jinx it.
Brewers yeast is what I was going to try, before I changed the meal schedule.