It may not be the dogs, but the dust and pollen that they collect, on your outings. You keep them all in long coat, so they pick up more dust.
What would they think of being vaccumed?
or light coats when you are out, and just wash their legs more frequently...
I would never give mine up, either, but they are picking up more dust this year than others. Not enough rain here to wash the pollen away!
Good luck.