I believe angels can possess their christian slaves, hence all the "Demonic possession testimonies" that get airtime on the jew-run television.
As for Demons, no they do not possess people, and i'm not sure if it'd even be possible. Their atomic vibration speed and frequency of bio-electricity is so high, that if they were to "possess" a human, we would incinerate. We may INVOKE Demons, but that is out of our free-will and they would never interfere in our lives without our permission or if it is to offer help to a Satanist consistently working dedicated for Father Satan.