In the event this raises questions in the validity of a family with adopted children, I would like to point out that family is not confined to your blood relatives; rather, it's a shared experience of living. I live with three other girls, and I would consider them as much my sisters as my biological sisters (had I any). But it doesn't even have to be the shared experience of living together; when I worked backstage in high school, I had a family in the people I worked with, spent time with, shared joy and frustration with. Family is much more than a nuclear unit of Mom, Dad, Jane, and Billy.
I don't think it's responsible to suggest that some people you live with would have the same rights to you, your possessions, and your life as the family you grew up with. I suppose that's the defining factor: growing up and coming of age. Yes, there are all the legal definitions that [necessarily] allocate resources and responsibilities. Those are important, too, in our society.
I write this thinking about families I know with adopted children. It's no big secret to them, and as far as I know my friend has always known she was adopted. She has had contact with her biological mother, starting when she was 18 (which I believe was the mother's stipulation). And that's that. The two other children in the family are biological, but she has no less claim to her parents' affection.