What is the theme of the westing game by ellen raskin?

There are many themes for example:

Family
There are two kinds of families in The Westing Game: the family you choose and the family you're born into. Westing doesn't just leave his estate to a relative; he creates a game of strategy that will help him find the best heir possible. If his estate ends up with a relative, that's great, but it's not a requirement. Similarly, Turtle forges a strong relationship with Flora when she realizes she won't get the kind of maternal care she needs from her own mother. In contrast, though, the sibling relationships we see in the book are really tight. Theo takes great care of Chris, and Turtle looks out for Angela. What we see there is a lot of love and support.

Wealth
Money always makes people act funny. That's especially true in The Westing Game, though, where the money in question is $200 million, and both an inheritance and people's lives are hanging in the balance. For some of the characters, money represents freedom; for others, education. Some think they won't be anything without money, and some are almost too eager to give it away. The characters are nearly all willing to lie, gamble, or steal to get it. The novel provides cautionary warnings about the damage having or wanting money can do, and it also raises the question of who deserves wealth.

Appearance
One big idea of The Westing Game is that people aren't who they appear to be. People are both literally and figuratively in disguise. Significantly, appearances have the power to limit people whether they seem to be, objectively, positive or negative. Angela's just as metaphorically restricted by her beauty as Chris is literally hampered by his disease. Many of the characters make judgments about the others based on how they appear – your outside determines whether other people see you as pretty, ugly, ordinary, or weird. But there's also power in letting people think you're something you're not, and the easiest way to do that is by changing what's on the outside.