(Here I usually insert a 'best of luck' closing, but I suspect you already have plenty).

I suspect the latter.Those of us with a lot of Landlord experience have heard these same excuses over and over.

The tenant states that he is concerned for the safety of his two little ones.I've notified each complaining tenant that they need to call the police if they suspect illegal activity and have talked to the accused tenant several times about correcting the issues until now with the drug related accusations.My wife recommended that we start a formal complaint process via mail which will eliminate the phone calls (and drama) and assist with documenting the complaints. 

In addition to door sets, I would suspect your entry door to be a dead bolt.Not all retail lock sets are easily rekeyed to work in a key tree (Weisser "smart key" is an example).

If that gets you the "deal", THEN you can decide whether it really is a tear-down-then-develop job, or a genuine rehab/flip opportunity (I suspect: tear down)...

But it has a multi-level structure to it, so I suspect the broker fees are very high.

I suspect most HOAs disallow short term rentals, but that's just a hunch.

I've found a fabricator and they want to sell me their quartz slab for what I'm sure is a reasonable price ($1110), but I suspect they're getting it from a wholesaler nearby and if I could just buy the slab myself I could probably save myself several hundred dollars.

I don't know whether it can delay eviction; I suspect you could argue that it should not, since the tenant is indicating the rental unit is not safe for the child(ren) so they should want to get out of there ASAP to someplace safer. 

However, I suspect we will qualify, and if so, I still think it comes down to a comparison of the ROI of the two scenarios which seems to favor RE investment, but with more risk.