Found: Kids' mystery with blackmail and murder - similar to Westing Game but not

I am trying to think of a book I read in the early 1990s, intended for middle grade readers. Whenever I describe the plot to someone they think it's the Westing Game, but it is not.

Plot summary: A wealthy man invites a lot of his famous friends to his mansion (maybe on an island) for a big party. One of the guests is his wife's niece, who is excited to be there despite the wealthy man not wanting her around.

At the start of the party it is revealed that he is blackmailing each of the guests for different reasons. Later that night or the next day he is murdered and the book becomes an Agatha Christie style whodunit, given that all of the guests at the party would have had a motive to murder the host. I think the niece eventually figures out who the killer is but I'm shaky on the details after that.

Thank you!

I'm wondering if this might be one of the 1990s 'Clue' books that were a tie-in with the board game. The only one I ever read was Who Killed Mr Boddy? by A. E. Parker (1992), and I don't remember enough about it to say whether it matches, but it's a possible lead.

Thank you so much for your suggestion! I don't think this is the one I'm thinking of but I really appreciate you taking the time to comment.

Moderators, looks like this one got solved by Tracy over at Stump the Bookseller: The Name of the Game Was Murder by Joan Lowery Nixon. (URL: http://w1.loganberrybooks.com/stumpthebookseller/376y-the-whodunit-on-the-estate...