Families have always been engrained into our cultures over the years. Being an adaptation that has kept humans around for all these years families have been involved in some sort of way. It is the natural way that we have grown as a human race. The family is different though depending on where you are from in the world, and you may have very different views of what a family can involve or who is a part of your family. The way someone grows up can determine who they may call there family, biology may not be the only factor that people determine who is in their family.
Depending on the culture that you are brought up into your view on the structure of a household may be different depending on your culture. In China it is common for multiple generations to live in the same households. In American households it is common for parents to send off their teenagers off to college and expect them to begin to support for themselves after, college and start their own lives in their own living spaces.