So you fill it out for him (he is actually your sponsor and the I-864 is a sponsors document). Under 5.3 "Persons NOT sponsored in this affidavit", I think you don't enter his spouse (you) because in fact he DOES sponser you.
But I even believe you (he) has to file the I-864EZ instead of I-864 if he can answer all three question below "yes"
Part 1. Qualifying to Use Form I-864EZ
1.a. I am the petitioner of the family member sponsored on this affidavit.
1.b. I am using my own earned or retirement income, which is documented using Internal Revenue Service (IRS) Form W-2.
1.c. The sponsored immigrant is the only person immigrating based on the underlying visa petition.
https://www.uscis.gov/i-864ez