Is there something I can give my bunch that would help the cats that need help, but do nothing for the ones that don't need any help?
Nothing comes to mind.
It sounds like some need more/less bone than others, but I'm not sure how you would work that in since you feed ground.
Unless you give, say, a chicken wingette to those who have the soft stools.
I can't remember . . . were you also using the Vet's Best? Or, as the brain slowly engages, you were using it but stopped because it was causing problems?
The only thing I can think of, but I really don't like to suggest is, is add a little psyllium powder to the food of the ones that have soft stools. The problem with that is they also need a LOT of moisture with the food, because psyllium absorbs water, and you don't need their stool going to the other extreme.