Previously House Broken Dogs Peeing in the House?

I have a Llapso Poo and a Tibetan Terrier both of whom I have had for four years. About 6 months ago both dogs started peeing in the house when we aren't home. It doesn't happen all the time, but has become quite annoying. Note: they have a doggie door that they use some of the time.

After reading some answers to a similar problem it looks like I should take them to the vet and I will, but it seems highly unlikely that they would both have a problem at the same time.

We do occasionally have other dogs in the house, but all the dogs get along. I add a little people food (like chicken or egg in very small amounts) because they had both become finicky eaters, probably because I spoil them.

I'm really confused because they have been such good dogs and have access to a doggie door. Plus I am home most of the time since retiring two years ago. When I worked they never peed in the house. Their favorite spots for peeing seem to be dining room on or near a rug, near my chair in the living room and kitchen and in front of the couch by a rug. Although they love my husband I am their main care giver. Any thoughts?

By Marilynn M.