Just because one dog doesn't have issues with the food does not mean that the other two don't have issues with it. Maybe one of them can't handle or is allergic to chicken?
Some dogs are lactose intolerant and cannot handle any dairy. Could this be the case since you're feeding cottage cheese? Maybe the 3rd furbaby is not lactose intolerant, but the other 2 are?
Frequent switching between different foods can definitely be a contributing factor to the tummy troubles.
Good luck!! I hope you find a diet that is suitable for all 3
