There'll be an apology for "accidentally" doing the paperwork wrong, which a judge will say nullifies the sale.
Alternatively, the couple will just be sued for lots of random things, and will run out of cash defending themselves, forcing them to declare bankruptcy and sell the property.
And the city's own incentive is to be as harsh as possible toward unpaid property taxes. The quotes in the story from Jose Cisneros are consistent with this.
So even though the residents are wealthy, they are up against powerful institutional forces.
And while it's absolutely true that the legal system favors the wealthy, there are diminishing returns to being still wealthier. Beyond some point you can afford to have a competent lawyer on retainer and it's much harder to simply bury you in trivial stuff. It's not obvious that these real estate investors will be easy to push around.
I predict that unless an obvious loophole appears very soon, it will be cheaper for the homeowners to just buy the investors off.