From The Heretic Knowledge Vault
The power clique among the elves, presently holed up and hunkered down in Praenubilus Astu. The Great Houses exert their influence via the nominal governing body of the Elven Council, which Sarine confronts after her faith-shattering experience with Kawaii and Nookie. (Sarine seems to use the terms "Great Houses" and "Council" more or less interchangeably.) They generally try to avoid contact with smelly humans, leaving the job of patrolling human territories (in search of Errants) to the rangers like Sarine. However, the prospect of Ian and Meji having the book of the Lorenzel Excavations worried the Great Houses so much that they decided to go outside usual channels and send a military party led by Toren (aka "Lead Dead Moron") to retrieve it. This turned out to be a Bad Idea.
We don't know yet whether there's a one-to-one correspondence between the Great Houses and the various races of elvendom (Rinkai Erufu, etc.), nor how many actual Great Houses there are. We also don't know much about their governing structure except for the Council. We do know, however, that every 20 years they dispatch an ambassador to Tsuiraku -- or at least that's the way it has worked in the past, but they've decided to move up the diplomatic visit a little bit this time, owing to the Ian/Anilis affair. The current ambassador, one Rarune, had a one-night stand with the daughter of an important Tsuirakuan on his last visit to Tsuirakushiti, which is why there's a Meji.
Note that Sarine alludes to the presence of "lower houses" when she, Jon and Sara go calling in Praenubilus Astu and are "invited" to address the Council. We don't know enough yet about the governing system of the elves to know the difference between a Great House and a lower house. Patience...