If they’re assisting in an exorcism they’re believers.
Quite the contrary.
They are there as non-believers who have reached the conclusion that the behavior of the person in question is NOT due to mental illness.
There's been a good bit written on this by psychiatrists recently. Have you not read any of it?
Not contrary. Basic logic. if they are participating in exorcism they HAVE to believe. If they didn’t believe they wouldn’t be participating. It IS mental illness, schizophrenia, delusional behavior, and a little munchausen by proxy reinforcement coming from the exorcist.