If it is difficult for you to get the other secondary evidences, you may 叫國內當地派出所或街道委員會出個家庭成員關係證明,證明你與你父母的血緣關係,然後去公證處作個公證. 這個公證可以作為secodnary evidence and also provide the two or more affidavits as the tertiary evidence. I think this should be enough.