The IRS apparently never considered the possibility of a U.S. citizen or resident alien who is required to file Form 8615 and whose parents are foreign. They do not provide any instructions or guidance for this situation. Several SuperUsers and a forum moderator discussed this recently and could not come up with a solution that we're really satisfied with. The best I can do is to suggest the following, with thanks to another SuperUser, macuser_22, who suggested this approach.
First, a couple of screens before the filing status question that you are asking about, TurboTax asked whether your parents are filing a joint tax return for 2016. Answer Yes to that question, even though they aren't. That will eliminate the question with the three options for filing status. When it asks for your parents' taxable income, enter zero. That is true, since they have no U.S. taxable income. Leave all the other income questions blank. Also leave your parent's Social Security Number blank. When the error check tells you that the SSN must be entered, just click Continue. You will not be able to e-file. Print the tax return. In the space for the parent's Social Security number on Form 8615, write NRA (for NonResident Alien). File the return by mail.
