Baths? Soap? What is considered too often?

So I know it's pretty uncommon for someone to bathe their chickens, especially if they aren't on their way to a Poultry Show or County Fair. However, my chickens live in my house and are spoiled. They are bantam cochins and are caged - wire flooring, but newspaper is placed on the wire so it doesn't hurt their feet. Sometimes they track their poo(you know which one I'm talking about, the wet, brown, extremely foul-smelling one) all over the newspaper, and eventually they sit all over it and climb on each other. Every two weeks I bathe them: warm water and whatever shampoo/soap I have on hand(sometimes it's Head & Shoulders, sometimes it's an antibacterial body wash). What kind of soap is too harsh for them? Should I get a specific poultry shampoo? Dog shampoo? And when is it considered TOO OFTEN? Am I ruining their skin? Feathers? After the blow dry, they get mealworm treats.

THE REASON I BATHE THEM:
They sleep in our bed(yes you heard right, my chickens sleep in our bed). They are still young(maybe 3 months old), but they are off the warmer.....so they LOOOOVE to cuddle under the "covers." Their covers are a dark colored, old t-shirt. They're small enough to fit on one half of the shirt, with the other half covering them(that way the poop doesnt get on our sheets). They stay in our bed once it gets dark, til it's time for us go to bed, then off to the cage they go. This is just until they don't like the covers and prefer the perch instead. Our other chick took 4 months til it preferred the perch over its blanket.