I would just give leave them a note saying you are interested in buying and include your first name and cell phone number only.
Don't tell them you are their neighbor and don't give them additional information. If they refuse to sell, contact the police or humane society.
The police where I live don't do anything, even if horses are dieing. There was this one guy with 30 starved horses and it took over 3 years to get any action. He was allowed to keep 10 horses, and that was after 3 horses died. I tried buying the horses off of him, and said I would help him sell (which meant halter breaking as some were untouched). He wanted thousands of dollars for his failed racehorses, and was completely delusional.
Absolutely buy them if you can. The police can turn things into a drawn-out mess with a bad resolution.