> My spouse income is less then 125% the poverty line, can my father -
> in
> law sign affidavit of support, or they bove have to?
Your spouse must be your sponsor and sign a I-864 regardless of whether
she meets the income requirements.
If she does not meet the requirements on her own, her father may be
your joint sponsor. He should sign a separate I-864. Unless you all
live together, in which case you can opt to have him sign I-864A.
Depends on whether he is considered to be in the same household as you
and your wife.