Thanks for your reply, and the picture. From what I can see, it looks very suspicious of a bacterial pyoderma (skin infection). It may also have an underlying cause, such as allergies (fleas allergies, food allergies, or other allergies), mites, etc.
It's good that you are using a topical flea product, like Advantix - keep it up!
Unfortunately, none of the possibilities can be ruled out, since you don't have any problems yourself.
You can certainly try the medicated shampoo twice weekly, along with the Benadryl to see if there is a positive response to treatment. If there is not, then Remy really needs to get back into the clinic for additional treatment (i.e. further testing, stronger antibiotics, longer treatment time with the antibiotics, etc.)