On the death of your final parent, the Capital Gains would have automatically triggered then. At that time, you would hav3e been required to obtain quotes from 3 real estate professionals stating fair market value as of that day. The difference between the purchase price, minus the cost of capital improvements (new roof, etc.) would be the Capital Gains. This would then set YOUR Capital Gains clock to zero.
Since you've only just sold to your son, get quotes now. The cost for doing so can be a deduction.
As I understand it, your purchase price 15 years ago was for HALF and was $38,500 making the total price $77,000. Unless you are living next to the Sydney Tar Ponds, darling, you and I both know that there is no way your real estate devalued by $7000 in 15 years. If you and I know this, so does the tax man! They don't give a rat's rear end that you chose not to make a profit by giving a family member a break.
Get the quotes, figure out what the Capital Gains are and start setting money aside. Gather your receipts for any capital improvements that you made, too. This is a 2007 transaction, you have until April 30, 2008 to claim this (unless you are self-employed, in which case you have until June 15, 2008).
Tax preparer for over 30 years. Never had a single "bad" return for any clients.