"If these things are not demons, then what are they?"
What LisaRose said. They are mentally ill and acting out. Plus you have to realize that 99% of what the Witnesses say are urban legends and that miniscule amount that may somewhat have happened is the person's imagination.
"But every once in a while...one comes along that just creeps me out".
Which means that the person stating it is creepy himself or maybe suffering from sleep paralysis where vivid, morbid dreams are so realistic that some people think it actually happened.
But like the second story, 4 elders, physical damage to the Kingdom Hall, visits from HQ regarding it? I'd feel foolish DENYING it happened.
The so-called 4 witnesses to the act might as well be part of a made up story. The story may as well include the whole congregation observing the situation.
Here's an example of a Christian Fundamentalist describing what is probably a sleep paralysis episode that he went through.
https://www.youtube.com/watch?v=pGTD5wL3mBI&feature=player_detailpage