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I am sorry to hear about this situation. In the end, your aunts have the right to tell your grandfather their opinions. They have free speech to tell him what they believe, i.e. whether what he wants to do is a good idea or not.
You can send a letter threatening to sue for interference with an advantageous business relationship. The elements of a cause of action for tortious interference with an advantageous business relationship are (2) defendant's knowledge of the existence of the possible contract; (3) defendant's intentional inducement of breach of the the possible contract; (4) the absence of justification; and (5) damages resulting from defendant's wrongful inducement of the breach. See Fields v. Cummins Emp. Fed. Credit Union, 540 NE 2d 631 - Ind: Court of Appeals, 4th Dist. 1989 (internal citations omitted).
This would be a weak case however, since they do have a right to their opinion, but the letter may scare them enough to keep away, regardless, if they do not call the bluff.
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