Given correct entries, TurboTax will correctly determine the taxable amount of these distributions.
What is the code in box 7 of these Forms 1099-R? Is the IRA/SEP/SIMPLE box marked?
If the IRA/SEP/SIMPLE box is not marked, is the taxable portion shown in box 2a of the Forms 1099-R?
If the IRA/SEP/SIMPLE box is marked, it would seem that you have not entered your year-end balance in traditional IRAs that is needed to prepare Form 8606 correctly.