Grandma left us her house on the other side of the country. We can't afford to keep it or even rent it out (rent prices too low, maintenance too high from far away). So we're trying to sell it.

When the neighbors heard, they offered to buy it. Three of them got together and basically jerked us around (contractors, finding money, etc) for almost three months (in the summer!) until they finally gave us an offer so low it was offensive.

We politely declined and - made a HUGE mistake - by telling them if it didn't sell, we might reconsider. We listed with a realtor who's held several open houses.

At each open house and every time any one of the neighbors is home to see someone expressing interest, the neighbors approach the potential buyers and start telling lies about the condition of the house - how it's been kept, the problems it has, etc.

What can we possibly do to stop this? It must be illegal...but we don't have $ to sue...any ideas for discouraging this long distance? Thanks!!
Additional Details
I guess I should clarify that the neighbors NEVER actually step on to the property - merely approach people as they park their cars on the street (some times in front of the neighbors' house(s)) and walk up on the public sidewalk.

The realtor is aware of the problem and has stopped holding open houses, but the problem continues as the neighbors intercept folks.

A restraining order for a number of feet when the neighbors involved live right next door and directly across the street seems unlikely and unworkable.