Use this form to show they have adequate means of financial support and are not likely to rely on the US government for financial support. You, the sponsor (petitioner), and the joint sponsor must complete Form I-864.See tips for completing Form I-864. If you have a joint sponsor, they must also complete Form I864. An Affidavit of Support sponsor must be at least 18 years old and must be either a U.S. citizen or a lawful permanent resident. In today's video we are going to be filling out form i 864 the affidavit of support form for the joint sponsor. This video will help you to fill out I-864 For Joint Sponsor. In this guide, we will explain who needs to complete Form I864, when to file it, and how to fill out Form I864 stepbystep. Complete this form entirely in English. 2. Attach the documentary evidence of support as explained below. 3.