The only time I encountered a problem like this was when I had a young, hyper cat that I kept locked out of my bedroom at night. Every morning while I showered, he would sneak into the bedroom and pee on my bed to punish me.

If your vet found nothing physically wrong, I suspect your girls are punishing you for something. Have there been any changes in the household lately? New pet, new baby, new roommate? Sometimes it can be over something that seems very insignificant to us. But if you can identify it and address it, the behavior may go away like magic.

When I let my kitty back into the bedroom (pouncing sneak attacks and all) he never again peed on the bed or anywhere in the house.