rehousebreaking

Question
I have two female North American Shepherds (mini-Aussie) that I bought as pups, from a good breeder.  They are now seven and eight.  They trained easily and have never been a problem.  Suddenly, they have both become un-housebroken.  They have a dog door, and have always used it- I don't take them out.  Now, they use the living room floor.  They know they are wrong- act all kinds of guilty about it, I tell them to go out, and don't let them back in while I clean up and later, they do it again.  Sometimes not for a day or two, sometimes several times a day.  I feel like they are trying to tell me something, but I don't know what.  As far as I know, nothing has changed.  If it matters, I also have two cats, who use the same door, and their behavior has not changed.

Answer
It could be a medical problem such as diabetes or hypothyroidism,it may even be that just one of the dogs has a problem and the other one just thinks it's ok to go inside since the other one is-so have them both checked by a vet,just to make sure

Also sometimes a change,even a very small change in the house,like a new rug or furniture will sometimes cause dogs to go in the house-sometimes it causes a dog to become upset,usually if that's the case they will stop doing that in  no longer then three weeks