The other advice in this thread seems good. I’ll second that providing numbers would be helpful.
I have a park on propane and it isn’t so bad. It’s definitely inferior to natural gas and is more expensive to operate, but not hugely so. If an HVAC pro tells you he can do the conversion for most of the homes, you may want to crunch some numbers on how much more a typical resident will be paying monthly for propane vs natural gas service, and then apply a cap rate to that increased cost. (if any homes can’t be converted you may have to buy a new furnace or water heater)