Thanks for not asking an unimportant question. You are the primary sponsor and will complete your own I-864. Because you show not self employment on a tax return yet, your current income is zero. Dad is the only joint sponsor, completing an I-864. Mom is his household member and completes an I-864a whether she has income or not.
Then, there is the issue of Dad's household size. If you filed your own tax return in 2019, it makes no sense you are your parent's dependent on their tax return for 2019. If were not claimed in 2019 then you are not part of your parents' household size, even if the expect to claim you for 2020. 2020 tax returns are filed in 2021. Perhaps that's a point of confusion. Please clarify.