That is the point a spirit becomes a demon. This process is described for current humanity in Romans 1 by Paul.
Romans 1 doesn't say anything about a spirit becoming a demon. I just read it.
All spirits reside with God. You can read about them in 1 Kings 22:19-25.
1 Kings does not say that all spirits reside with God. I'm afraid you're basing a lot of your understanding on things that are just not scriptural.