Roxy and TJ are almost 4 years old. I have been battling this for 3.5 yrs. Trust me ~ I have tried EVERYTHING....This has now turned into a behavioral issue.
What is currently working is a
very special treat for no poop eating. The treat is so good, that they come to tell me there is poop to flush
(this took time though)
Reese's Peanut Butter Chips (from the baking isle). They both get one chip when "I" get to pick up poop and flush it. And they never get this treat for anything else!
I know this may not work for you since you have a handful of pups ~ as I only have Roxy and TJ ~ But I have learned to behaviorally treat their poop eating b/c mine are definitely eating it due to behavioral reasons now after all this time.
I have also started to walk them every morning (so there is less boredom during the day)
Best Luck and I hope you can find something to resolve this nasty habit!