movie

hey, I've been trying to find this movie for a long time noe and i can't find the name.  its about a group of friends and one of them are brother and sister i think. they are going on a road trip and on their way they meet a lady. the lady told them they could stay at her house if they could help her find her son that disappeared in the woods near her house.  they said yes but when they got to the woods one of them disappeared into this invisible portal where everything looked the same and she or him i can't remember could see the others but they couldn't see her.  eventually everyone goes into the portal and finds a cabin, later one of them goes crazy and they have to put him outside in a robe i think.  i can't remember much after this, but i do remember there was more portals and one of them everything was completely dark, and the sister goes back for her brother, but she gets killed because the brother is dead/ possessed. can somebody help me find the movie name ????