My 2 dogs are big housedogs, I will NEVER put them outside at night to sleep. They sleep in my room on the floor, and normally, I bathe them 1 or 2 time a month, it depend how dirty your dogs are. You don't want to give your dogs a bath everyday or every week or something like that, it will dry your dog's skin.. I would say 1 or 2 times a month, it would be good enough.
My dog, Copper, the red (Shepherd/Dingo mixed), he likes getting in the bathtubs, river or lake and he get dry skin, and I used my son's lotion and oil to sooth his skin. He is a waterdog and LOVES to get in the water...