If your parents are in US, and they will file I-485, then they need: their birth certificate, marriage certificate, your birth certificate. Because some IO may not trust the Chinese birth certificate as the proof of the family relationship, If you have the 戶口本 which has your name and your parents' names together, you had better do the 戶口本公證. If you don't have such the 戶口本, you had better the family relationship 公證