The Strange House is actively haunted by the ghost of a young girl, the same one who appeared on Marvelous Bridge in Pokémon Black and White. This ghost intentionally arranges furniture to force the player to enter various rooms. The player is able to leave the house at any time, though. At the end, the player will receive the Lunar Wing.
Basically, every time you enter a different room in the house, the furniture will be in different places, so just go into the rooms you can until you can get to the Lunar Wing, which is in the middle room on the second floor.
If you’re still lost, this video shows you exactly where to go.