Unfortunately, this is a situation where there is a manipulation of the mind by long-term spirit possession to inculcate the characteristics and communications of a prior spirit meddler infestation. This has resulted in a situation where an ongoing presence is being sensed and can interact with him dynamically in response to his very thoughts. So this, to him, seems completely real and reflecting an outside consciousness that is present and can respond to what he is doing and will be able to perturb it and create a backlash, for example.
This is impossible for most people to discern as being of their own manufacture because it is simulating the opposite quite accurately in the way this mechanism works, and will be a perpetual problem until enough healing catches up for this to fade. Whether that can happen will depend on his ability to let go of the belief it is a real, active spirit possession underway that is simply intractable. The degree of perturbation and unhappiness with the state of affairs, unfortunately, are providing great negative energy serving to reinforce its presence. It is much like scratching an itch and having the itch grow to the point where it is impossible to stop scratching because the rebound effects become intolerable.
In order to correct this, he needs careful coaching and support and subconscious channeling with trauma resolution to further accelerate the ability to heal what is essentially an imprint on the mind of the spirit presence but it is sort of like having a subpart of the mind, as created by trauma, that is more than the repository of memory, but an actual dynamic mimic of a set of criteria and characteristics such that it can carry out a dialogue with varying script elements. When approached and questioned by the conscious mind, it will display the attributes of an independent entity and this will be quite convincing to represent an outside interloper when, in fact, it is the remnant of outside interlopers to create this internal persona for purposes of self-tormenting.
It is unlikely he would cooperate with an advanced process of this kind because of its highly unusual nature, and his level of skepticism is keeping him rooted in the prosaic approaches where, to him, seeing is believing, and he would need to witness and feel this directly in action, which is not possible because it is a subliminal process altogether and would require faith on his part to keep going in support of the work. And that will be very unlikely to happen given his level of skepticism about remote work in general and marginal belief in divine healing, given he has not found relief despite many promises.