Douppleganger... Need Help?

I've tried to post this twice now, all I need to know is what is this thing that is messing with my neighbors.

I was the first one to see it, it looks exactly like Zack. This happened months ago, when I was walking up the driveway, I looked into the kitchen window. I could have sworn that he was leaning over the counter in a t-shirt facing the bathroom. I knew it was Zack because he's the only 6'5" guy in the house that's tan and dark haired. There was something off when I looked inside though, and it was unexplainable. Instead of walking through the kitchen to get out of the rain, I went up the balcony stairs and into his room. When I saw him, he was wearing a dress shirt and dark jeans looking the like the complete opposite of our friend who was staying the night with him. It freaked me out, and I questioned both of the guys assuming that they were messing with me. I knew, though, that they were telling the truth and was just hoping that I didn't see what I did.

Last night he came back. Zack had fallen asleep early and his roommate couldn't sleep so he went outside. When he came back inside he saw Zack standing over Zack. There was sleeping Zack and then there was another Zack leaning over him in a striped shirt. He stayed there for hours, whispering to the sleeping Zack. This caused Zack to say "mommy" multiple times.

Eventually Chris messaged him telling him about the guy standing over him, the guy I saw. He said it felt evil and that Zack needed to put on his protection necklaces. Zack only got the message describing what he saw, and when the sun came up with morning, he got the other part. After Chris sent the message the figure ran out of the room and went outside.

This allowed Chris to sleep, but throughout the night it kept coming back and waking up Zack. All he could see was its face. It had a black featureless face with white lips. It told him to "join them".

We all know their house is haunted by a few ghosts but we're not sure if this is a ghost of demonic entity. If someone can tell us any possible information about it, that would be a great help. Thank you so much.