I suggest locking the person to their slot on civ, the lock being released when the server restarts. I'm not fully sure if you can, but maybe create some type of parking area for 2 cars? A garage or a driveway? Maybe introduce a house key too, so only people with that key (copies can be made) can enter, but a max of 3 copies if that's possible. I also suggest Designated areas of the city for different types of civs (Functionaries next to civ spawn, doctors next to hospital, Profiteers next to industrial park etc.)