Since it's in Tulsa, Oklahoma I'm thinking about electric baseboards for heat.

The utilities are separately metered except for the heat which is oil.

One tenant pays 1100 and other pays 900 and heat and water paid by landlord.

I would switch over to a heat pump if your climate would allow it.

Boiler heat with most of the piping missing.

I'm not home much so I can turn off the house heat during the business day into the evening hours.

Situations will differ based on terms negotiated.A condo is an element within a building where the unit is owned.

All that being said, chainging to individual HVAC untits will allow you to get away from th eold boiler and get the tenants paying for heat. 

The problem I'm having now is that the water softener which was kept in the garage at the property was apparently leaking and for some reason the tenants removed it and put it outside in the desert heat to rot. 

Maybe just say you are taking it off the market until the heating issue can be resolved, and offer to let them apply now or later when it is ready to rent.