Father Jackleg (1972)

A con man inherits a gold mine. Knowing that his family are even bigger con artists than he is, he assumes the mine is worthless, and teams up with a partner in a scheme to unload it on some unsuspecting chumps. However, the other members of his family discover that the gold mine is actually worth a lot of money, and they set out to take it from him before he realizes what he has.