You posted the same message in another thread and were advised to consult a tax professional. One of the reasons being is you do not appear to have a good handle on the difference between the federal gift tax schema and the income tax schema; they are completely different and need to be differentiated.
For one thing, you need to look at your purported $250k fair market value solely from the standpoint of gift tax and preparing and filing a gift tax return (Form 709); that valuation has nothing whatsoever to do with the income tax consequences resulting from the sale component (i.e., the sale to your parents).
On Form 709, for example, your gift will be valued at the fair market value on the date of the gift less the outstanding balance of the assumed mortgage (depreciation deductions you have taken do not factor into the value of the gift). You should definitely have a certified appraisal done for the valuation on the date of the gift.
Per Section 1.1015-4(a), your parents (the transferees) will take a basis of $110k, which is essentially your adjusted basis since $110k is greater than the $100k outstanding balance of the mortgage (they are assuming)
This should get you started, but you do need to consult with a local tax professional as there are other issues, including state taxation.
