This clan has been influential since at least the '50s. Back then, they were one of the Emperor's major doppleganger suppliers; we don't know if their power base has shifted since then, but they were about the most powerful clan around. When the Nirduk, Shorin, Balan, and Parnos clans were considering starting operations against the spiders in AK 592, the Parnos were based in the mountains surrounding Auramkil, but they later developed a presence in the city itself as well. They universally dislike the Shorin, who are responsible in part for the current animosity between the humans and elves of Auramkil.
The Parnos clan went underground in the mid 590s, and even Lady Ylena did't know where they'd vanished to. Kelmin has heard rumors that they're in trouble with a group of demons who become very powerful at night (Silvana speculates demiloths) and that Azuriel is on the southern continent.
In late 595, the party learned that the Parnos had made contact with the sea elves, and together they were involved in some kind of operation with a faction of yuan-ti.
Caedon was the head of the clan in the '50s.
Caedon's niece. Back in AK 555, Solera was going to be married to Ganeth Barshen. Since the Barshen needed an alliance to fend off the Nirduks, and the Parnos needed a new doppleganger supplier, it was a match made in heaven. Must be why the Nirduks (with a probable assist from the Shade Lord) derailed the wedding by killing off the groom and his entire family (or so everyone thought for a few decades, anyway).
As of early AK 596, word is that Solera's based on the southern continent and does a lot of adventuring with dolphins.
Azuriel is the current leader of the Parnos clan. She is generally considered to be old, very sly, and firmly devoted to good; she's also reputed to continually watch for weaknesses in whoever happens to be around her. She claims to get along well enough with Hajmola. When the clan leaders met to discuss those anti-spider operations that never happened, she had a "mostly spirit-like thing" hovering behind her; Ganeth thought it was probably a spell effect, and it was possibly an invisible and gaseous person or guardian creature; in any case, the thing was Neutral Good. Lady Ylena believed that Azuriel was visiting the southern continent during the Vault escapades, and Kelmin thinks she may be there now.
According to Ylena, Thellana is one of Azuriel's subleaders, a priestess who doesn't care for fighter/mages. She's apparently a priest of Corellan...and since as far as we know he's blocked from the Prime, the obvious question is, where are her powers coming from? (Since Asmo and the Temple of the Nine Jewels may both be involved in Corellan's problems, I have a bad feeling about this...)
Zillandor is Azuriel's other subleader and seems to be a pretty cool guy. The party met him in Breepul City, where he was on a quest to kill Inquilla, the true shade who'd previously killed him.
There's a good chance the party sent Inquilla down the rift they opened in Silverton, so it's unclear what the status of Zillandor's quest is. Unfortunately, it's also unclear what the status of Zillandor is, though it's probably not good. The party had gotten Zillandor to attempt to return the body of an abducted locathah princess (who the party had accidentally killed while taking out the sahaugin ship where she was held prisoner), in hopes of preventing a war between the locathah and the mermen. They later learned that Zillandor's meet with the locathah was ambushed by undead; since then, Zillandor has not replied to sendings.
Elissa is Ganeth's intelligent longsword. She was crafted by the Parnos a long time ago (she has no real sense of time, so it's hard to know how long ago), and while she's usually very outspoken (especially when Yves was around with his evil orcish spider-slaying broadsword), she tends to be silent when the Parnos are around so they won't know she's there and reclaim her. (Since Elissa's favorite partners are noble high elven fighter-mages, Thellana might not be too sad about the sword being "missing," but who knows?) Lord Rognukena mentioned that whoever broke her out of prison during her visit to Auramkil had a sword that seemed to be Elissa's twin.