Does the priest with the Gospel and the cross affect a jinn possessing a human?

There is no impediment to priests and other leaders of disbelief influencing jinn that possess human bodies. This falls under the category of humans enjoying jinn, as mentioned in the Almighty's verse: "And their allies among mankind will say, 'Our Lord, we enjoyed one another, and we have reached our term, which You appointed for us.'" The jinn enjoy the obedience and worship of humans, and humans enjoy achieving their aims and the jinn serving them. Furthermore, this tempts the weak-hearted and the ignorant among people, leading them to incline towards disbelievers and to approve of their false doctrines. This is part of the jinn's enjoyment of humans by beautifying the path of delusion for them.