While usually foils come in pairs, or a couple of pairs in The Westing Game, we see the players – that is, all the heirs except Turtle and the Judge – work as a large group of foils. This might seem unconventional, but in a text with such a large cast of characters, many of whom have small but pivotal roles, it makes a lot of sense. They're united by their shared desire to solve the mystery. We learn more about each of them in and through the context of the other players, as we watch them, and they watch each other, approach the same endgame from vastly different places. By the way, while Sandy fits here as one of the foils, by the end of the book we realize he's been an antagonist all along.