who do you talk to when you get all their votes?

If i recall correctly to the guy in Tel Mora, the one whose private rooms you can reach only by levitating from OUTSIDE the tower.

Hm... i thought it was the guy in Tel Vos, not sure anymore about this.

When you start the Telvanni horator quest you're supposed to talk to the librarian in vivec I believe, at which point you are given a book which lists all the members you need to talk to. Also may require visiting the floating guardhouse in vivec. Anyway eventually you should get a book. Same goes for the Redoran as well. The books have a title with color being a part of the title, red book of something and brown book of something.

I'm a member of house redoran, the telvanni didn't like me at all. I wound up bribing a number of them to sway their vote.