You need to figure out who the sponsors are. It is it you and your husband then you can use his income to sponsor your dad. As to the proper forms, read the instructions carefully. Your dad is not your husband's immediate relative and hence you should meet the standard income requirements.
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You are the petitioner you have to sign the I-864 regardless of your income. You husband will have to sign I864A if you want to use the family income to sponsor your dad.
I agree with Ms. Grinberg. The petitioner on the immigrant petition is the one to sign an affidavit of support. Your husband is a household member and needs to sign I-864A. When I tell you this, I assume you file taxes jointly. If you do not, he will have to file a separate I-864 as a co sponsor.
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