If the petitionner has been unemployed for the past 15 years, she is 84 years old US citizen.
Does she have to complete the I-864 on behalf of the intending immigrant, if she has a joint sponsor who will file the I864 and I864A?

Hi Jean,

According to the below, both petitioner and joint sponsor have to complete the Affadavit of Support:

http://www.uscis.gov/portal/si...CM10000045f3d6a1RCRD

Who can be a joint sponsor, and when is a joint sponsor allowed?

If the visa petitioner's household income is not sufficient to meet the requirements of INA section 213A and 8 CFR section 213a, INA section 213A permits a joint sponsor to sign an affidavit of support, in addition to the affidavit of support signed by the visa petitioner. A joint sponsor is someone who is willing to accept legal responsibility for supporting your family member with you. A joint sponsor must meet all the same requirements as you, except the joint sponsor does not need to be related to the immigrant. The joint sponsor (or the joint sponsor and his or her household) must reach the 125 percent income requirement alone. You cannot combine your income with that of a joint sponsor to meet the income requirement.

Thank You.

It does make sense.