Just realized this issue myself. And after spending days editing a new save changing over houses and families, too. Even with getting the vanilla pets off gallery and returning them to premade households, getting a Mayor Whiskers and a ghost Whittaker only household is impossible. They had this error 5 years ago as well, apparently.
I'm gonna have to wait for a fix before starting a new save file all over again... The least the devs could do is create a method/cheat to have animal only (unplayed) households and leave it to player discretion to recreate a mayor whiskers and ghost whittaker, if just to fix when this error occurs.
