House Trained Dogs Peeing Inside?

My Maltese dogs are 4 years old, (Max and Chloe, brother and sis). The past year they started peeing in the house when I'm gone. It started when I had my niece stay at the house to take care of them which she has done since they were pups.

Now when we are away on vacation and sometimes when we are just out for a few hours they leave their mark. I make sure that they urinate before we leave, they both seem well drained, but still seem to squeeze some out while we are gone? I don't know what to do.

By Mary