to be deductible as mortgage interest the property must be security for the seller-financed mortgage.
since no 1098 has been provided, the instructions for a schedule A mortgage deduction with no 1098 require the seller's name, tax ID number, and current address.
another issue you face is the amount of interest paid. The IRS will match this to what the seller reported. if they don't match expect issues with the IRS. if you can't provide the required info, expect the IRS to deny the deduction or send you a letter requesting the missing info. you will also need to complete the Home Mortgage Interest worksheet in Turbotax if the mortgage exceeds the allowable maximum of $750K
