Real Estate contracts normally have to be in writing and signed to be binding under a doctrine called the "Statute of Frauds", which requires certain contracts, including contracts for the sale of real estate, to be in writing. If your sister could prove she changed her position financially to her detriment based upon your oral representation, she might have a claim but it would seem pretty doubtful. Unless she paid you for the right of first refusal, I think she is unlikely to successfully mount any legal challenge to you selling to the other sister. That's the legal analysis; the practical side is the first sister will likely get mad over all of this. Ask sister #2, with whom you have nothing binding legally, if she would help you try to maintain some semblance of family harmony by offering it to #1 but with a written contract to be signed, to close within 30-40 days. That may smoke out that #1 really can't buy it anyway...if she won't sign a contract, and put down a deposit, move on to #2. Good luck. Family messes are always the worst.
Answered on Mar 08th, 2013 at 3:32 PM