This is my only rental property.I'm contemplating selling the property and taking my profit for a few reasons, but one most of all.I would say my property is in average, a bit above average condition, but certain things are a bit dry or dated, no central A/C for example.

I believe that Hem Fir is what they make the kiln dried stuff out of (at Home Depot).

Here in the smokies, people did great last year doing this…so far this year i think it has dried up very quickly. 

Properties take longer to rent, rent stagnates or deflates, credit dries up, banks tighter on loan rules, credit cards decrease credit lines, your credit score drops because instead of 30% utilization you overnight go to 50-80-100% when they drop your credit line, hard money dries up for flips, stock market goes down and you don't want to take losses or can't use margin.   

Is there anyway their hairs, sons/daughters, 20 y/o “husband” can become protected tenants upon their passing?  

Wife and daughter don't like them as they make it hard to clean their hair of shampoo.

Sometimes you can tell because of rust staining and buildup on the outside of such affected pipes,   but even without that they can be weakened considerably from their original state.On the drain side galvanized branch drains  (1.25 through 2" galvanized pipes)  can also rust out or clog up as the rust on the inside is very rough and catches hair, grease,  and other debris and will eventually need aggressive rootering,   which if the pipes have rusted enough may open up holes in them.I should note CAST IRON (hub and bell) old sewer pipe,  at least the 3" and 4" stuff seems to have a bit longer lifespan than galvanized steel;  it still rusts but doesn't crumble and flake and encourage blockages like steel does,   so an old house with a cast 4" sewer stack you may be fine for many decades more if you just replace all the branch lines going into it but leave the main stack.   

He also had gray hair and a few decades under his belt.

I hate to pull the grey hair card but 20 years of collecting rent is 20 years, how many years have you been handling rental properties?

Again I am playing the REALTOR hair because I have my license, however a wholesaler would just communicate to a licensed real estate agent of what to say when an offer is given to them.