IMObservation, whether your family says couch or sofa depends on what your parents (and their parents) always said.
We always were--and remain--"couch" people. (AE)
I can remember as a young boy hearing another kid refer to sitting on their sofa. I knew what "sofa" meant, of course, but I wondered what the real difference was. One day I got to see their "sofa," and, as it turns out, it was very much like our couch.
In my youth we would never have used the word "settee." We could have figured out what it meant (couch), but we might assume that it must have been bought with lottery money (or something like that). That is, for us, "settee" sounded like a too-fancy word for couch.