The percentages that you should enter for your premium, your SLCSP, and your advance payment should be an amount that everyone agrees upon. It could be 34/33/33, 50/25/25, or another amount.
Just make sure you are in agreement and that the percentages on all tax returns add up to 100% together. The program will calculate the information that should be on your return based on your answers.
For more information, see this TurboTax FAQ: I'm on my parents' 1095-A form. What do I do on my return?