In most places heating is required for a dwelling to be considered habitable, and you'll probably get a lot better tenants if you have AC in Jacksonville as well to mention that it should help keep mold at bay better than nothing, If I were you I'd cough up the money to put in a new HVAC system.

Or would I change my investing habits and diversify my portfolio to be less heavy in rei?

We don’t know any PMCs to recommend in the area mentioned, but since selecting the wrong PMC is usually more harmful than selecting a bad tenant, you might want to read our series about “How to Screen a PMC Better than a Tenant”:https://www.biggerpockets.com/member-blogs/3094/91877-how-to-screen-a-pmc-better-than-a-tenant-part-1-services-and-processesWe recommend you get management contracts from several PMCs and compare the services they cover and, more importantly, what they each DO NOT cover.

We don’t know any PMCs to recommend in the area mentioned, but since selecting the wrong PMC is usually more harmful than selecting a bad tenant, you might want to read our series about “How to Screen a PMC Better than a Tenant”:https://www.biggerpockets.com/member-blogs/3094/91877-how-to-screen-a-pmc-better-than-a-tenant-part-1-services-and-processesWe recommend you get management contracts from several PMCs and compare the services they cover and, more importantly, what they each DO NOT cover.

Its not harming me or the neighbors.

Perhaps a dumb question - but is the property habitable right now? 

People live up there year round so it's safe and habitable all year round but a very different environment.

@Jeff Langley No harm in recording the option, a memorandum of it anyway, to prevent the seller from selling to someone else.  

Let them stay...no harm, no foul...they are not breaking their agreement after all.

Cars are owned outright (older but good vehicles) cable television was cancelled, insurance policies reviewed, spending habits assessed etc.