[Edward to Bella:] "No, not many. But most won't settle in any once place. Only those like us, who've given up hunting you people" – a sly glance in my direction – "can live together with humans for any length of time. We've only found one other family like ours, in a small village in Alaska. We lived together for a time, but there were so many of us that we became too noticeable. Those of us who live…differently tend to band together." (14.35)
Edward's family is indeed rare. Not only do they not eat people, but also they can have a semi-permanent home, since they aren't, you know, killing their neighbors. This comment also implies that vampire families are, in part, bound together by their diets and morals, rather than by being biologically related.