Didn't you submit your birth certificate to the USCIS when you applied I-130 for your parents? if not, ask your parents to make your birth certificate that includes both your parents name and your name with your birth location. If your birth certificate is in Nepali language, do not forget to translate in English and also certify it with authorized personal in Nepal and submit both to USCIS. Other than that you really do not need any affidavit from other people. You only need affidavit, if you do not have your birth certificate and you can not make it in Nepal.