It's been awhile since I've messed with a lot like that, but here goes! First, make the lot residential (if it isn't already). Then open up the cheats panel and type and enter: testingcheatsenabled true. Then type: buydebug. This will open up a new type of buy objects menu, with a question mark on it.
Look for grey orbs in the new buydebug panel called hidden room marker and public room marker. The orb will not be visible during game play, but it will change the way sims use the room it is in. Place hidden room markers in the rooms you want the NPCs to live in. Then shift click on the doors to those rooms and designate the room for NPCs. NPCs may or may not move into the building depending on story progression, not sure how to force them to chose those rooms though.
For the areas like the bar that you want everyone to be able to use, place the public room marker in the room. For areas you want only your own sims to be able to use, place no markers.