The couple probably asked the residents to buy back the street for some exorbitant price (like a cool million). If they had only asked for double their purchase price which is a very reasonable number, the residents would've taken the deal I suppose.
I don't think the residents can reverse the sale, but making the wrong type of people your enemy is not a good thing, unless you have the resources. The residents can dig into the dark secrets of the couple (everybody's got them) and turn the table around if they find interesting evidence. It may not be that hard. I doubt the couple is living a pristine life outside this purchase.
The couple should have set the price high but not that high for the residents so that it's not worth their time and efforts to fight back. After all it's just money.