Anyone who took longer than three seconds to be sure that Elissa is Rachel's sister needs to be voted out IMMEDIATELY. Same build, same hairstyle, same hair colour, same face, save voice. Don't think we hear Elissa laugh yet, but I'm sure that's the same as Rachel's as well.
Less obvious is how Nick is related to Dan Gheesling (Season 10 and 14). Fairly similar looking and almost identical voice (JUST too loud along with the oh-so-doltish delivery).