I would recommend fish oil daily. I use the Grizzley Salmon Oil-pump bottle. But you can give the same fish oil to your dogs that you would take for yourself.
We use a humidifier in the winter months, the house gets really dry. It helps all of us. Just make sure you clean the unit often and replace the filter.
I personally think you are over grooming.
What shampoo do you use when you bath them?