Looking for a video (please open to read)

I’m looking for a video I remember seeing a long time ago. In the opening scene, a boy is spying on his mother and father having sex in a living room. Shortly after, his sister arrives and catches him; she then starts spying on their parents as well, and the boy begins fucking her while they both watch their parents. Later, the scene shifts to a staircase—similar to the one shown in the photo. That’s all I remember.