Aside from nice full-on side adventures like Mad God's Key and War of the Wielded, has anyone run some smaller side plots involving the Scarlet Brotherhood in Sasserine?
The one player in the campaign who has so far given me the most background is a scarred, one-eyed swashbuckler, once of a noble family who was loosely allied with the Sea Princes. They were murdered by the Scarlet Brotherhood nearly a decade ago (when the character was a young adolescent) with the uprising against the tyranny of the Sea Princes, and the PC survived only through sheer luck (though the Brotherhood assasin wounded him near unto death, and that's how the PC lost his eye). He survived miraculously and was sheltered and hidden by Heldrath Kellani (who, being a social climber and a slippery political mind, had once considered marrying her young daughter Rowyn to the PC), and now lives a migrant existence hiring out for day work on the docks... watching the comings and goings of merchants and traders, keeping an eye on the Scarlet Brotherhood and noting their actions, and so forth. Moreover, the description of the Brotherhood embassy specifically says that they built the structure "over the site of a noble villa whose members were slaughtered during the final years of the Sea Prince rule" -- perfect setup for a vendetta.
(On a side note, I can hardly wait to do some sociopolitical backplot and lay the foundations for Kellani's reveal to the PC, and of the PC's secret identity as one of the then-despised noble family that allied with the Sea Princes) at the end of TiNH. *evil grin*)
That, plus a half-elf monk PC with an anger problem (custom flaw) (who I'm hoping to angle in the direction of "learned his kung fu from a stolen Brotherhood codex"), suggests a substantial presence of the Brotherhood is well-warranted. Having read up on their Wiki entry, the Brotherhood is pretty much a great villain -- an Aryan-eugenics, slave-driving, expansionistic and militaristic ubermensch villain, at that.
I had a SB side plot, where the SB was helping the PC's, against the SB. There are many factions in the SB, the one that has established the embassy with Sasserine wants to expand through diplomacy and trade, whereas there are other factions that still want to conquer, others that want to go back to secrecy, and others to piracy, ect. ect.
The scenario started off like this. The harbormaster had 3 younger children in Sasserine and the module said nothing about what happened to them when the harbormaster was assassinated. So rather than killing them, I had them be taken by the assassin (who was hired by the Lotus Dragons as per the module, I suspect the assassin may have been Todd Vanderboren from SCAP, but my PC's never found out) to the Lotus Dragons who then later sold them to the SB. Vark had a contact with the SB as per the module. The SB was interested in them because most Sasserine nobles are of suel blood, therefore they would make great breeding vessels and such. Naturally the Embassy SB got wind of this, and asked the PC's to help, so that the SB would look good to Sasserine by ratting out it's own rivals in the favor of Sasserine.
So the PC's agreed, had a rendevous with a SB slave ship that had the children on it, and did a basic shipboard assault, and in the SB slavers final throws they released some creatures they captured from the nearby jungle.
Interesting take on it. I hadn't even considered the three younger daughters of Islaran... though of course, now that you mention it, it's completely possible that they were in the process of being recruited via the prestigious Telvanta Academy. A wee bit of brainwashing and a year or so later...
Of course, what could make this even more twisted and political is if Keltar Islaran himself had ties to the Scarlet Brotherhood. If Rowyn knew this, and could at least provide some evidence to that effect, it might provide some interesting counter-arguments to the PCs when they bust into the Lotus Dragon lair. "You fools! Are you truly so naive as to believe the Scarlet Brotherhood has intentions that are good and pure? Do you know nothing of their history, the people they've assassinated, the nations they've conquered and enslaved? The Lotus Dragons are the best line of defense Sasserine has against their treachery!"
Don't forget that there is a Scarlett Brotherhood team on the Isle of Dread. Being a player I don't know the details, and I think they were left pretty barren as far as information and background, but the island goers might be another opportunity to bring the SB into the picture. Maybe even as good guys.