Are you a dog being wagged by its tail? Most are.
Fighting the damned. The damned are as prone to influence as they are able to influence others. So though they may scoff at modern religious concepts, mind tricks can disturb them enough to weaken their hold on our world. They are prone to suggestion, can be deceived by illusion, and are even easier to deceive than regular humans are in some ways as they don’t see the material world directly.
A magician sounds like a good exorcist for them? Yes, or someone with exceptional intuition.
A simple way of exorcizing both a ghost and a ghoul is this. With strong enough intention, you can set up a scenario like they knew in life. You treat them like they are a dinner guest. You have to do it with total intention, rid yourself of conflicting imagination, but you go through your dinner routine, and you set a plate for them. You eat dinner like you normally would, focusing entirely on your dinner, and when you are done you focus your awareness on them and tell them that dinner is over and it’s time for them to leave, and then you remove the food you served them from your home. Ghouls are hedonists, so you hit them below their belt, make them feel human for that moment, and they lose their grip.
Vampires on the other hand were jaded in life, intellectuals. The trick with them is to set them up as liars, dramatize inconsistency in their habits and cycle. Vampires can’t handle ennui, meaninglessness.
Now from time to time a spirit of the land will aid the damned that dwell there. They have an affinity for that state of human existence, and they organize the spirits so they have a better shot at enduring.
Can someone who is possessed tell that it’s happening or does it seem normal if the entity resonates with them? At first, it seems normal, but the person becomes less and less conscious. They stop remembering things. A favorite tactic is the alcoholic black out, but high stress works too. Over time, they can push someone into a hormonal state that lets them have control almost constantly and more or less permanently. This is why mania is associated with cannibalism. Mania is the ghoul psychic signature. Jeffrey Dahmer would be an example, though his companion likely saw himself as more enlightened than other ghouls.
The reason communal ceremonies like religion work, as compared to magickal techniques, is that at one time the religious ceremony had the psychic or spiritual energy of the entire community behind it, but it still wasn’t foolproof.
The depth of exorcism as a discipline is actually rather vast. Too much so to handle in its entirety in a reasonable amount of time.
You mentioned angels possessing people. Did that happen often? Yes. There is a long category of miracles associated with it. If the stories are true, then it still happens from time to time. Some spiritual workers function almost entirely in that way. It was said to be the influence behind Edgar Cayce.
What about Joan of Arc? Yes, though in her case it was just below the threshold of possession. She was overshadowed, as I have heard some call it, constantly in communion, but not serving as a direct vessel.
Your thoughts are welcome. Be well friends.