Remind those neighbors that the sale price of your home is their comp moving forward. Wether they are interested in selling or not, most people don't want to lose equity or value in their home. They must really like you as a neighbor and want you to stay. good luck
You also might share a story with the neighbors about another deal in which the seller's neighbors did something similar, and the seller retaliated by placing a tenant who did stuff that drove those neighbors nuts.
How is it that the nosey neighbor is able to speak with the potential buyers that view the properties?
I suggest that the listing agent speak with that neighbor to determine why he is responding this way and discuss it. Point out to him on how the sales of these homes on his street may benefit him and his home. Perhaps, then the neighbor's view may become more positive so he won't interfere anymore.
Best of luck!
Prudential Connecticut Realty