Exactly what valkarath says. If it were possible and they can take over human bodies and just be demons on earth (and they completely would if they could) the oldest and wisest would have no reason to assist us in our acension as the human form would be on their path.
We can incarnate from different planets, realities and realms, this is possible, but I digress.
And you’re not crazy. Symbolically speaking the demons will say things like ‘you are a demon.’ All of the time.
If you you’d like to learn the truth about your past and heritage, I suggest study in accessing the Akashic records, although if you are not ready for it Metaron and it’s council will not let you in.