Yu Suzuki's team at Sega released some screens of all 4 Chi You Men a few years back. But here's some info on them:
http://shenmue.neoseeker.com/wiki/Chi_You_Men

This message has been deleted.

no guys, they already revealed that her brother Zimming is 1 of the 4 Chi You Men and he is the West leader = White Tiger, Lan Di is East = Dragon, South is Niao Sun a woman who represents phoenix and North = turtle and snake is an older man yet to be revealed perhaps the Chi You men leader.

Yeah I twigged at that point. Seemed like the obvious connection, Theres lots of loose ends and connections yet to be tied up since theres no shenmue 3 yet =[

i think they hinted at them being siblings in the second game which allows more in a 3rd game if they ever make it
i don't remember if ryo told Xiuying who he was after but i think she knew exactly who land di is and what he is capable of
maybe she wants ryo to stop him to stop her brother before he does something terrible again
and im 100 percent positive ryo would spare Lan Di, he would prolly come close to killing him and think about it, but he'd realize he would be no better then Lan Di if he killed him, he would sink to his level and thats not what ryo would do or want since ultimately he has a heart and i don't think is willing to take a human life
thats why i love the shenmue storyline, its incredible, i wouldn't even mind if they turned it into a film

I agree. One thing I noticed was Zuming appears to have a scar on his cheek (as does Lan Di) I could be wrong though as the flashbacks are in that sepia effect which makes it hard to tell. I'm sure he does have a mark or a scar though.
Plus it would make things far more interesting when Ryo finally gets his chance to kill Lan Di.
Which brings me to another point: do you think Ryo will kill Lan Di, or will he spare him?
I think if he does turn out to be Zuming then the final confrontation will see him defeated by Xiuying