Hi,I would suggest to check DOS website they have lot of detail abt chargeability.Anyway,the best supporting document would be their birth certificate from state of chargeability...if that is not available then any record at the time of birth like hospital record etc would work.
This is a copy of DOS website"REQUIREMENTS FOR ENTRY
Applicant must be a native of one of the countries listed below. See “List Of Countries By Region Whose Natives Qualify.”
Native of a country whose natives qualify: In most cases this means the country in which the applicant was born. However, there are two other ways a person may be able to qualify. First, if a person was born in a country whose natives are ineligible but his/her spouse was born in a country whose natives are eligible, such person can claim the spouse’s country of birth provided both the applicant and spouse are issued visas and enter the U.S. simultaneously. Second, if a person was born in a country whose natives are ineligible, but neither of his/her parentswas born there or resided there at the time of his/her birth, such person may claim nativity in one of the parents’ country of birth if it is a country whose natives qualify for the DV-2007 program.
Hope this help!!!
