A yacht club perhaps--you can build it on a beach lot and use 'hood decor for the yacht part of it.

Ii is actually not that easy: royals and nobles mostly went to the king's palace for balls and extravagant parties. Interests were probably hunting, horse racing, bloodthirsty activities (like the "sport" at the Colosseum in Rome), watching plays at the royal theatre, visiting each other, planning wars with the king and trading slaves. The eldest son would inherit the land, the second son would go into the military, the third one into the church.

So whatever you build them, I'd think you should add underground basements so that they have a place to hide when the revolution arrives

Not sure why I keep thinking this, but you might try the vocational training controller from Paladin. Then you can build a lot in such a way that it will seem like the house of representatives. Also, with the visitor controller paintings, go with one for formalwear so everyone at the lot will have to be in their formal suits.

An upscale spa maybe? With hot tubs, saunas, massage tables, salon chairs, etc? If this is supposed to be historical, maybe call it a bathhouse and use the hot springs instead of hot tubs?

House of representatives with a feudal king - I do not believe they existed; the king had all the power. He (or she) had advisors, but they were probably corrupt too (well, I guess not all kings/queens were corrupt back then, but they did believe in the God given right to rule because of their not so healthy bloodlines) - the ordinary people were not represented until later in time (after the French revolution - oh, a real revolution - wink, wink).
I like the bathhouse idea. Didn't the Romans do that?