I don’t read the Bible literally in every respect. I think a lot of it is symbolical, allegorical, &c. I don’t believe that God ‘made the world in seven days’, or the snake-in-the-garden story, for instance.
And I don’t believe in demons, beyond their existence in human imagination - which can become very ‘real’ in effect, if you dwell upon the idea ‘religiously’.
In the world of facts, you can say with some certainty that certain things exist or do not exist (and even then one can be wrong).
But the world of belief is quite a bit different. What a person believes may or may not be accurate. Things that exist are independent of one's belief.
The other day, I had a friend tell me that he doesn't believe in hell (or God for that matter).
I told him that it doesn't much matter what he believes. It he dies and finds out that there is indeed a God and a hell, he will not be able to use the excuse that he doesn't believe in them.
Hell either exists or it does not.
In other words, demons may exist (or not), but what you believe is irrelevant to their existence.
There was a lot of fill in the blanks done, no doubt. But the essence is what matters.