I was having problems too with one of my yorkies.
I beleive it was related to food allergies also, grains in particular, and if i'm correct (please someone correct me if i am wrong) there are grains in Royal canin too.
I then found an great dog food food called Orijen made right here in Canada (alberta!) that i reasearched about. I found (one of the very few retailers) here in Quebec and odered from them.
My babies all love the food, i'll never go back nor switch!
Has great smell to it, no grains, 70% meats,
and a plus they have nice firm black poops
My yorkie who was having skin issues has made a 80% improvement, they all have nice-full shiny/soft coats, i am really impressed with orijen.
Anyways...lol i think i've blabbed enough...
I wish you well in finding the right food for you and your babies!
Here is the link... go and visit their website!
Orijen Pet Foods: About ORIJEN:
Good luck!