Documents to Prove U.S. Domicile. If you want to sponsor someone for a family-based green card, you need to provide proof of a U.S. domicile in your Affidavit of Support (Form I-864).Obtain Your Visa Document. To complete Form I864, the petitioner must meet certain requirements. We will need to see original or certified copies of documents for identity and U.S. citizenship. Campuses are encouraged to document eligibility directly to the extent that relevant information is already on file at the campus. Learn how to prove your U.S. domicile for a family visa with our stepbystep guide. Essential documents and tips to ensure visa approval.