Now, for the human filler. These characters aren't really essential to the movie, but there are a bunch of other McCallisters traveling to France.
They don't play any really crucial role in the movie, but they're listed in the cast: Sondra (daughter of Uncle Frank), Jeff (Kevin's other brother, who says "You are such a disease!" to him) Rod (son of Frank, who Buzz tells about Marley being a serial killer, as Kevin listens), Brooke (who doesn't say anything at all), Tracy (daughter of Uncle Rob), Georgette (Frank's wife), Uncle Rob, and two unnamed cousins.
Uncle Rob is Pete's brother, who they're all going to visit in Paris—which makes him sort of important. But he doesn't actually have any speaking lines in the movie, making him seem rather less important.
Take away? These guys are way low-key.