Thanks a lot. We are able to find a neighbor's daughter who is living in the US. Since we grew up together, we may be able to ask her to write a letter to prove the relationship of my parents and me. Is it necessary to do so? If so, a casual letter is sufficient or there is a formal template we need to fill out?
-Had better ask the local Chinese Security Department to issue the letter, and then ask your friend to translate it into English (not need to do the notarization if it is urgent).