There may well be zoning laws, that restrict how many people can live in a place with a certain amount of floor area.  In many places, though, these rules aren't very restrictive.  But it's certainly worth looking into.You can't pin the blame on your neighbor, for people standing in the middle of the road, even if they are his tenants.  If it's a chronic condition, you might want to complain to the police;  be prepared for some hostility when the tenants find out it was you that brought the cops around.