Chester's the biggest treat snob in the world.
And now with his allergy to poultry, it just makes things even harder.
What I've resorted to is buying thin slices of meat (pork or beef) when the prices are slashed for quick sale because they've reached the "sell by" date. I cube these and cook 'em up with a tiny bit of garlic powder for extra smell, and just use these for training treats. I actually did some work with him tonight with some of the chopped pork and it worked great. Sometimes I cook up some ground buffalo as well but keeping some big chunks in there to use as treats. It has more aroma than beef and Chester usually will go for it.
Just a thought your doggies are treat-finicky.