Telvanni has I think two surviving Members. One guy lives in Riften (The dude you set up to join the Thieves guild) and the other, is the girl dunmer in the College.
IIRC Brelyna mentions having family who sent her to the College, so it's more than just her and Brand-Shei. My guess when it comes to Brelyna and her family though is that they're descended from House Telvanni, but not exactly "members" since the House itself basically ceased to exist with the Argonian invasion.
The implication I've gotten from Skyrim along with The Infernal City / Lord of Souls is that, basically, the Great Houses we knew from the Third Era are gone. Kaput. Scattered. There's descendants all around, such as a few mer with the surname Hlaalu, and there's a few Sarethis (same name as one of the ruling families of Redoran) around as well, but they can't exactly claim membership in a House that doesn't exist anymore. Of the Houses but not in them, if that makes any sense...a bit like the descendants of House Dagoth were in MW, really. (Well...the ones that weren't lurking about in caves, noshing on corprus flesh, that is.

)
My guess is we'll see new Great Houses (or smaller clan-sized ones) spring up soon, if there aren't some already. Maybe not in Skyrim, but certainly back in Morrowind and on Solstheim as well.