Since more than one of them is itchy, it is less likely allergies (although still very possible if they were on RC). I'm sure you've read that it can take 2-3 months for a new to take effect. You can try a prescription diet (
) if you think it's food or go to one with limited ingredients and do an elimination diet. It could be environmental allergies or dry skin. Since more than one has the itchies, it could be mites. When in doubt, go to the vet. If it is determined to be food allergies, steroids short-term may help them get over this.