First option, it says nothing as to cash-4-keys, lease buy-outs or incentives tenants to voluntarily leave, in summary as long as your trying to "buy" out a lease for "voluntary" leaving a property, it's nothing but air & opportunity. 

Try pouring water from pots directly down the tub drain and see if you see water.

I don’t know about having that many hands in the pot for a STR, that can be difficult.

Only if the owner plans to owner occupy, or have family member occupy out of housing need, then tenant must leave and can be evicted if don't voluntarily leave.

As a previous HOA President, you'll most likely need to wait until the next election cycle unless you can convince the board to voluntarily leave. 

Now, if the occupants voluntarily surrender possession to you (help them to volunteer with a cash incentive), then you have a case where they have given you some rights.

I think the may have been growing pot or something as the utilities dropped sharply after they moved out. lol

You could sweeten the pot by paying him interest .

Or I like the idea of doing a few potted shrubs - could leave them for the buyer to plant in spring.

And no, the NRA is not a well regulated militia -- it's a group of people who voluntarily pay dues to associate at-will with others who share a common interest.