I don't think you should assume that everyone is comfortable confronting or even communicating with their neighbors. You don't know them and you don't know their neighbors. There are times when it is better to have a neutral third party investigate the situation.
If there is a law against beehives in this neighborhood,, the bee people should hear about it from the city. What makes you think they would believe their neighbor?
This situation is making me think of that movie with Tom Hanks, and the weird neighbors.