How to stop my cat from peeing in the same spot?

My cat is about 6 years old and is an indoor cat. Every night she keeps peeing in the same 2 spots. We clean her litter box often and she will use it during the day but when everyone is asleep she goes downstairs and pees. I wake up to her pee every morning and is wondering how to get her back to using her litter box. I have one other cat and 2 dogs. She never had this problem but for a couple months now its been bad. Any ideas?