Quoted from HandsOfStone:I have talked to a real estate attorney and he has told me it is a lost cause and we'll either have to pay him half, or have a court ordered split-sale.
Sounds like someone with more expertise than Pinside has already weighed in here. Best option would be to have a second attorney look at the details if you want another opinion. The only way to get out of that is to prove that at that time, she wasn't in a right state of mind to be agreeing to a contract...that's going to be really difficult, or impossible, 17 years later and she's still mentally fit.
Quoted from HandsOfStone:I have offered to pay him half of the value of the house, but of course he thinks it is worth WAY MORE that what the other houses have sold for in the past year.
Seems like an agreed upon 3rd party appraisal of the property would solve this.