Bill's corrrect. The investor can sell it to whomever he wishes.
However, the investor might be reluctant to do so out of concern that the bank might believe (incorrectly, as you describe it) that there was some collusion between you, your dad, and the investor. The investor might be safer selling to someone else. But that's the investor's call. If he's willing to sell to your dad, it's certainly doable.
Hope that helps.