I have "people" in my head too -- but they are usually not identifiable as individuals -- just the repeat of what people have told me over my life. They are thoughts; the most destructive ones are thoughts that question the validity of my own thoughts, or even of my very person. I certainly have gotten plenty of that over my life -- including from so-called mental health people.

I think this existence of "people" inside one's head is probably common, if not actually universal. We probably have to have many inside our heads to develop our own personality. Not ones we actually see, for the most part -- I have never "seen" any of these people really. But I personally think that even the ones that a person might see are related to what is more the norm. They are not something completely incomprehensible.