The other four have shared wall of kitchen (non-plumbing wall) and living room with fireplace.

Could you then maybe install a cheaper or even used ventless natural gas fireplace in each unit?

Large ensuite master bedroom with all the modern luxuries including a fireplace, window seat, and spa-like bathroom.

I have an older relative who uses one of those electric fireplaces so she feels warm, technically it is a space heater and not allowed but they look the other way. 

Here are the skills and lessons I learned during the rehab of my second rental.1.If the property has been vacant for over a year and still has fleas, there may be a raccoon living up inside the fireplace.

Waiting for a month with no rent is like putting the cash in the fireplace and lighting it on fire.  

Does anything exhaust out the chimney (is it being used or future use with existing fireplace)?

Living Room: Replace ceiling fan, remove ugly white trim above fireplace, install laminate (using laminate throughout house except for kitchen and bathrooms).  

If you don't want OSB for subfloors or sheathing, you can upgrade with plywood, I don't see the need...My $67 a foot includes extras such as, 9' first floor ceilings, wood burning fireplace, high hat lighting, upper tier granite kitchen & bath tops, hard wired for alarm system.

., Onsite wastewater treatment, 3-chamberHeating: Exhaust air heat pump and fireplace in each apartmentCommunications: Good bus connections.Environment / Nature: Lakeside!.