S2 visa application, family designation

I plan on visiting my cousins who live in China currently due to work relocation. I have finished the application for the S2 type, and have a letter of invitation from my cousin. My question is whether or not being cousins counts as a family member, and if I need to provide some form of family tree legal document. If not, what type of visa should I be applying for to visit them for about 10 days? Thanks