Rules
There were rules to being part of the Hamilton family, rules that were often unspoken, but nevertheless very clearly understood by each one of them, with implicit threats of serious consequence if they were breached. This never stopped the twins from trying and often succeeding in doing so, of course, but even the twins understood that some of those rules were never to be crossed, that under most circumstances, every single one of them must be followed. It wasn't just for their own good, for their own protection and safety that they must, but for that of the family, and even the twins, when it came down to it, wouldn't sacrifice their entire family for the sake of rebellion alone.
For one thing, there was the rule about never killing inside the house. That was a matter of practicality. If they had to resell the house again, as they inevitably would, it was difficult to scrub bloodstains out of carpets or tile, and if the walls were particularly thin and neighbors lived close by, they would undoubtedly hear any screams or witness any attempts to escape. In a related fashion, it was necessary when buying a house to purchase one with a basement or some sort of storage shed or garage, where any killings that weren't completely outside of the house could take place, and all the storage of the bodies and blood could be maintained in order to preserve leftovers as they needed. With Lenny now, and with the others when they were younger, there needed to be somewhere they could store him, somewhere he could have plenty of room to himself but could still be safe and contained until he was ready to come out, to follow the rules as they needed him to be able to. All these were matters of practicality, the basics.
Then there were the ones that were also important, but tricky at times to abide by, such as the issue of food. Never allow outsiders to see blood, of course, or to realize your attraction to it, your need for it. Keep food in your house, cook it and offer it to guests, and learn ways to disguise your own lack of partaking. And if the subject of those like you comes up, no matter how lighthearted the conversation, steer away from it as gracefully as possible. Never, ever let the word "vampire" cross your lips where another could hear it; it was altogether too likely they might begin to make connections that should never be made by someone intended to survive.
It was necessary, of course, to keep it all a secret. There should be no close friends, no romantic relationships, nothing that would allow someone else, an outsider, to draw close enough to really know you, to figure out who and what you were. They would never be able to understand, and they could never be part of the family; even if they had wanted to, the temptation it would cause you every time they drew close, every time you could smell their blood in their veins and hear their heartbeats quicken in a moment of passion, would undoubtedly become too strong one day, and disaster could happen as a result.
It was in every way intended to be a life of solitude, lived apart from the others and within only the circle of one's own…and this was why the final rule was the most important, the ones even the twins never dared to break. Family. Family was always first, all that mattered, the only people you could count on or turn to or allow yourself to feel any affection or attachment to, because when it came down to it, family was all you would ever be able to have for good.
In comparison to that, all the other rules could be cast aside, as long as you learned how to clean up after the disasters that would follow in their breaking.