Hi, you can authorize your relatives who are in Vietnam. Dossier to make an authorization letter can be made at the embassy
Fill out a standard affidavit of support for your aunt and also list out your assets including your home. Go to bank and notorize it. Then mail the notarized copy to your aunt in vietnam. Your aunt take her passport and the notarized affidavit of support to US embassy to get the Visa .
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