Their problems (real or imagined) are the ONLY problems that matter.

For 16 units, I'm imagining that's going to be at least $200 / unit / mo, which would almost completely eat up the current $3400 net cashflow. 

The pic below may help visualize, just imagine that the building takes up pretty much this entire 1A through 1D plot except some parking.So, for determining building from land value, what percentage could our little slice of land be? 

I'd imagine you could access at least 150k of your current equity, which would give you a hefty sum to work with.

I can’t imagine how I would feel if it happened to the children of one of my tenants.

I can't imagine any accountant would advise you to do this.

Can you imagine the outrage if the dog has been sold by a private person?

@Mickey Roberts read your lease; and all states have Tenants Associations of one kind or another; I do not know where you are located but do some googling- Fair Housing, tenant's union, HUD etc. you will find them and I would imagine they will assist you.

I imagine some commercial leasing agents might have some good data that can provide guidance. 

@Andrew Rowold  I'm not in Houston but hotpads.com, forrentbyowner.com and of course probably the most popular I would imagine is still Craigslist.