Is there 1 demon....

...or are there several?

There are implications that there is just 1 and other implications that there are more.

The guy on the audio recording says "I fear the only way to stop those possessed by the spirits of the book is by the act of bodily dismemberment," implying several demons.

Cheryl says "It's not going to let us leave," implying a single demon. (Although she would be pretty much oblivious to the amount of demons there really are)

Several people are demonically possessed at the same time, indicating the presence of several demons, although within this movie's universe, it might be possible that a single demon has the power to manipulate more than one person at a time.

What do you think??