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Hello, my name is ***** ***** I will try to help you. Please remember I just report or interpret the law, so the outcome may not be what you hoped for.
Did you have any communications by email, text or otherwise about how you would be compensated for the investments you put in the house? What did you tell your father in law at the time you made the investments? At the time he refused to sell the house to you what was discussed about his reason for refusing the sale or the money you had invested?
What state are you in?