Well, no matter how good the quality, not every food agrees with every single dog. If your three are so gassy on Canidae, it's certainly worthwhile trying them on a different high quality brand. You may well find that they like something like chicken soup or wellness a lot better too.
I wouldn't personally put them back on the Iams - it really doesn't have great ingredients. LOL - the top 2 and corn meal and chicken by-products. Beet pulp is also high on the list, and those ingredients are common allergens. Since allergies were the main reason for switching to a high quality food in the first place, I really wouldn't head back there gas or not

How are Bear's allergies doing anyway? Any improvement at all?