This was something I saw in the early 90's. Opening scene is a husband and wife who get busy on the couch in their living room. Next scene is sister at the door. At some point some friends come over and there is a scene in the kitchen between two women. Next scene is at the dinner table, the visiting sister is sitting between the visiting couple and she is touching the woman and the man. The visiting couple excuse themselves and end up having sex on the stairs.
Another scene involves the husband, wife, visiting couple and the husbands boss and wife out in the back yard. The visiting sister ends up in some girl on girl witht he bosses wife. That was as far as I got in the movie. Can anyone help me ID this film, it's driving me nuts.