Will to Die (1971)

An aged millionaire passes on and leaves his four children his large fortune. According to his will, the four heirs must spend one week at his estate in order to split up the fortune. If any of the heirs leave or die before the week is out, the remaining children will receive the money, and if all of the heirs are gone the servants will gain the inheritance. Once everyone has arrived at the estate and settled in strange things begin to happen and the heirs begin to turn up dead. Who is killing them and can the remaining heirs find out before it's too late?