All of House Charthagnion's country holdings have, of course, been confiscated. Their primary mansion in Westcrown has passed to Archduke Narikopolus's sister, who married into House Charthagnion thirty years ago. She's spent months wandering the massive house aimlessly, holding her grandchildren and looking at portraits of the dead. She is better now than she was a year ago, but she's unlikely to ever really recover from watching all of her sons die by the final blade.
The house is essentially empty, and the archduke has need of it. His sister is upset that the plan involves inviting Iomedan butchers into her house, but his sister can return to Menador and cope. He hires paid servants, has the place cleaned, moves in his own staff and advisors, and issues dinner invitations and offers of lodgings to those nobles he knows to be in the city for the convention. Offers to stay in the house for the convention's duration go to his own vassals, and to every Iomedan he can name who could possibly need it. Throw in some other returning expatriates of apparent Good character, too, if any seem likely to lack a staff and adequate lodgings in the city. It's important that he look out for his own, but the most important thing he can do on that front is to ensure that the company they keep cannot be rounded off to "all of the diabolist holdovers".