Can I level with you? If you work the "best" in with the Old Roy, gradually increasing the amoung of the good stuff, they'll eventually be converted to it.
Old Roy is made up of chicken beaks, snouts, and whatever's left of some of these animals, plus some filler and artificial colors and flavor. It's junk. It really is.
IAMS, Science Diet, Pro Plan, even Purina One is better than Old Roy. I've never run across a dog that didn't like Purina One.
Get rid of the hot dogs. Hot dogs don't contain the vitamins dogs need and are likely the reason they won't eat the "good stuff." If your dogs are fat, hot dogs are the reason.
Again, sorry if I was blunt, but my dogs are so much healthier since I switched them to Pro Plan; their coats are prettier and they don't go to the vet but once a year for their check-ups.