I haven't tested it recently, so I don't know for sure if they'll stay on the lot when you leave it, but the minion feature I added to my
Sorcerer mod was more or less built to allow you to keep npcs on the lot without running into annoyances. You can switch the minion between a few different roles (such as maid cleaning or guest) and you can command them to go into a sleep as well, so you're able to do the fastest game speed, even with them there.