uncontrollable heating in multi unit apt
The simple answer is to set the fan to on instead of auto. This will help even out the temperature during off cycles. Using the dampers in the duct system close off the damper to the apartment with the thermostat 50% and make adjustments to all the other apartments accordingly. Keep notes on how the dampers are set because this will likely be a seasonal change that has to be done when switching from heating to cooling.

Adding a multi sensor thermostat like an ecobee as mentioned in the comments will also help. But it won't eliminate the problem. You need to balance the air flow into each apartment. If the apartments that are normally cold are suddenly the apartments that are comfortable then the ones that were comfortable will suddenly be too warm. Try getting it sorted out with dampers and possibly adding multi sensor thermostat. The downside of an ecobee is that you have to change the batteries periodically in the remote sensors tekmar makes some hardwire versions but then you need to run a wire to each sensor. Changing batteries in a single dwelling home isn't such a problem but in a rental it becomes problematic. 

There isn't much else in the way of a simple fix you can do that I'm aware of. 

Side note

In my region multiple-unit dwellings require fire separation in between every apartment. If one duct system is used then fire dampers need to be installed at all fire barriers. I don't know if this applies to you but be careful when dealing with multiple dwelling homes.