The only ones can give the right answer is the owner's family. Only they know if he owes more money to the bank than the market value or exactly what is the reason that they do not want to sell it or they can't.
If you make an offer to the family that benefits them, then they may sell it to you. ...else, not much you can do if they do not want to sell or do not care what happens to the property. Is the home vacant or are they living in it? If they are living in the home they may be living for free, therefore have no interest in selling and/or moving until they ultimately have to.
A short sale is where the sale price is less than the mortgage and the owner does not have the difference to bring to the closing.
What does the contract say about walking away? Speak with your attorney.