Agree with all of the above here ethanryan. Your nan could be hounded out of her home by the pressure and stress of people like this, if you can come together to take action it'll be better in the long run.
wildwood really hits the nail on the head by saying that these people are relying on your nan's gentle nature and, really, age, in order to get away with being antisocial. I have such a lot to say about people who don't pick up!
But this isn't the correct outlet for that...!
As lankeela says, Your nan won't be named, so don't think, or let her think, she'll "get into trouble".
Good luck.