Where are you planning to do the tea ceremony? At FMIL’s home or at the reception/ceremony venue? Traditionally, I believe you first visit the home of the groom’s parents and offer tea to the groom’s family, then you go to the home of the bride’s parents and do the same. These days, a lot of people just have it immediately before or after the “regular” ceremony at the same venue.
Definitely do not wear jeans, no matter what your Fiance says! If his mother is traditional enough to want a tea ceremony, she might feel insulted if you were to serve the tea in jeans. A qipao/cheongsam would be great, but a good one is not cheap and will probably need fitting so if you can’t get one, a red dress will be fine. If you’re not wearing your wedding gown, do NOT wear a white dress. White is the Chinese colour of mourning.
I was told the person who runs the ceremony is usually an older, married, female relative, and you usually ask a younger female relative to help you with the tea pouring, tray holding etc. My mother says it was my dad’s relatives who ran the whole thing for her. Talk to you Future Mother-In-Law and ask her if she wouldn’t mind having someone from her side of the family do this. It really wouldn’t be fair to expect your relatives to know what to do!
As for the kneeling, this is personal preference. My parents have already told us that they would be really really uncomfortable with us kneeling in front of them. So we will just be standing, bowing and offering them the tea. They’re also not keen on using all the traditional titles to address each relative. You should ask Future Mother-In-Law if they’re expecting you to know them. This can be a nightmare in big families as each relative has a separate formal title.
Does Future Mother-In-Law have a special tea set for you to use? Typically, the bride’s family provides the wedding tea set but it doesn’t have to be very fancy.
I found this website with some info but it’s probably best to talk to your Future Mother-In-Law on her expectations before the big day: http://www.chinese-wedding-guide.com/tea-ceremony.html
For my own tea ceremony, we’re doing it the day after the wedding, at the same venue since it’s a Destination Wedding. I’m wearing my grandmother’s kebaya and my uncle is buying the tea set for me as a wedding present. Fiance is not Chinese, so we’re going to offer tea to his folks in their own language 🙂
Hope that helps!