Help with I864 - my dad as joint sponsor

Hello everyone! My husband and I are in our late 20s and together and individually we do not have enough income to qualify, so we are listing my father, who has been tremendously helpful and supportive throughout all of this, as our singular joint sponsor. We received a RFE for my previously filed I-864 because I only gave my dad's financial supporting documents but not my own; my reasoning was that I thought because I didn't qualify, I didn't need to submit anything, but I now realize that they need proof that I don't have enough income. My question to you all is: my father is still married and my mother and father file their taxes jointly. My mother for the past few years has been retired. Should I calculate my dad's individual income from their tax returns or do I use the AGI of both spouses? My dad makes enough money that he qualifies for the above poverty guidelines on his own but I just want to file everything correctly. My dad is the only joint sponsor but I have no problem filing an i864 for my mom as well if need be, I'm just a little confused. Thank you and sorry this is long winded!