With a forced air gas furnace, you typically have one central thermostat to control the whole system.  

Another solution, is to stick with the same configuration but couple a high efficiency replacement with programmable thermostats.

(depending on your market)Try to avoid an over under situation if possible, unless newer with sound deadening between the units,  i have  owned many of these and renters always complain if they hear the tenant above or below.Separate utility metering and thermostats eliminates a lot of tenant complaints also.

The building was occupied by the owner who lived in one of the units and had the thermostat that controlled the heat for the entire building in her unit.The heat for the building is produced by a single gas fired steam boiler which was installed last year when the old oil boiler was replaced.What is the best option for controlling the heat for the property?

While I am no computer programmer, (I'm the guy who calls support and they ask if it's plugged in...

I did have one tenant get frustrated with us because we locked the thermostat (put a cap on how low/high he could adjust the temp).

We have thermostatically controlled faucets in our bathrooms.  

My wife has been a computer programmer that has been saving money for 25 years or so.  

I would fix the leaky vents and thermostat and not pay the utility bill.

It's seeming like having a programmer build it out will be what I am seeking, but I don't think I can allocate the necessary budget to make it worth their time and effort currently.