For GC I submitted what was required. In absence of bc you can submit secondary and tertiary evidence. Which is school records, etc and affidavits by my parents. Which was enough during gc process. In this case my parents are part of the petition so they cannot write affidavits. Affidavits should always be written by third party who are not a part of the petition. Like relatives or people who had knowledge of the birth. In my case I have already gathered affidavits to submit along with rfe.