What’s the title?

Hey everyone. I’m tryna find a movie that I watched a long time ago that I cannot figure out what it is and I’m at the point of where I think I made it up lol. A group of friends stay in a cabin together, there is also a creepy guy next door who watches them. Then one of the friends reads like a journal and it’s about this guy who raised his kids in the woods but I can’t remember if it’s like raised as wolves or just as a murderer dude. But the brother and sister are friends in that group and once they realize it then the brother and sister start killing their friends off.