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When people share a Marketplace policy with someone that is not on the tax return, they must choose that it's a shared policy.  Percentages need to be entered for  your premium, your SLCSP, and your advance payments.  This is how the Premium Tax Credit is reconciled.

Currently, the Premium Tax Credit is based on your income, not the children's father.

Since your children have insurance on a shared Marketplace policy, both you and their father will need to enter a copy of the Form 1095-A. TurboTax will ask you questions about if the policy was shared with someone and how to allocate the costs and credit. 

The percentages that you should enter for your premium, your SLCSP, and your advance payment should be an amount that you and the father agree on. It could be 50/50, 0 for you and 100 for him (Since he's the one who may have received advanced payments), or another amount. Make sure you are in agreement and that the percentages on both tax returns add up to 100% together. TurboTax will calculate the information that should be on your return based on your answers.

Once you change the percentages, You should see a difference.

To enter Form 1095-A refer to the TurboTax Help article Where do I enter my 1095-A?