First of all, what your wife said the value was in 1996 is meaningless. You need a professional appraisal (not a real estate agent's estimate) as of her brother's date of death. A professional appraiser can give you a retroactive appraisal.
You need a lawyer to examine the relevant documents and figure out when and how your wife actually acquired the property. It's not clear whether it was an inheritance, gift, purchase, or something else. What the old deed or title said might not establish actual legal ownership. Who was the other owner? Why did the other owner not contest her acquisition of their share? You might need both a real estate lawyer and a tax lawyer.
