The clear and obvious answer would be to instantly pay the back taxes and offer a small lump sum for them to move with and just lowball in whatever structure works for the both of you weather that is a better sale price or a greater monthly payment to them and just find your middle ground that works out for you both.

The value of that place would go up $100K instantly with the new look.- Cabinets look good but I'd get rid of all the clutter above.- Take all the cheap prints off the walls. 

In 4 months….Honestly, best case scenario is you are turning your money instantly and you will then end up making 30k/year.

I'd look at doing an FHA 203k or a homestyle renovation loan to add some instant equity on your next purchase!

I can confidently say that these "master classes" and courses claiming to grant you instant success are mostly deceptive.

Instant equity gains after the build is complete, easy to manage, high demands. 

You're literally forcing instant gratification when you're at the 20 yard line.

Depending on how long it will take to complete the remaining work and get the property sold, you could also try to find a larger general contractor; one that could self fund the work in return for a higher payday at closing.  

It wasn’t a huge payday—$5,000—but what I gained from the experience was far more valuable than the check.It started when I got a lead from an older woman who owned a house in New Hampshire but lived in Maine.

Occasionally one does a good enough job that the wholesaler makes a nice payday (for him) and you get a good deal.