The Sanzo title, I believe, is passed on by convention when the current holder dies, but I don't think it has to be that way.

I'm almost sure Koumyou suspected something, if not knew outright. I also think Ukoku had a major hand in the killing--either because he couldn't let someone else have power over him (via understanding) or because of sutra-y things. Minekura will reveal? *G*