Hi

I had a very similar problem a while ago. I have two rescue cats and the female one begain peeing on my bed a few months after we got her...
You have to make sure that you get rid of the smell of wee. Cats are creatures of habit and will go back to the place they have used before. I had to dry clean the duvet, wash all sheets and scrub the mattress to get rid of the smell. Also I tried a product I got from the vet - I can't remmeber the name but its like a plug in air freshner but emits a calming smell for cats - this seemed to work.
I would suggest just keeping all the doors closed to the bedrooms and see if its just a passing phase - it was with my cat - fingers crossed!