Suggestion

If it is difficult for you to get the other secondary evidences, you may 叫国内当地派出所或街道委员会出个家庭成员关系证明，证明你与你父母的血缘关系，然后去公证处作个公证. 这个公证可以作为secodnary evidence and also provide the two or more affidavits as the tertiary evidence. I think this should be enough.