Last week my mother's niece (also her biological sister) died...and I was once again reminded how this whole adoption thing makes my family slightly difficult to explain.
My mother was adopted by her maternal grandparents. To me, it's simple. My grandparents are the people who filled that role. While I have a relationship with her bio mother, I consider her to be my aunt. Perhaps it would be different if I had known her growing up, but I didn't meet her until I was grown. So, to me, mom's bio mom is her sister. Her bio sister (who was raised by bio mom) is her niece.
To me, it's not that complicated. In my worldview, genetics has a role BUT relationship is far more important. So, I don't have any reservations about considering the family relationship to be that of the role that they fill in my life. Apparently, though, this offends some people...
I have an ongoing debate (perhaps argument would be more accurate) with someone that I know about this issue. He gets quite upset that I call my mom's bio mother my aunt, rather than my grandmother. When I talk about my family, he actually corrects me on their titles.
I will grant him the fact that he was raised by his grandparents, like my mother. However, in his case there was no adoption and the genetic titles were reinforced sternly. In fact, he was scolded if he called his grandmother "Mom". So, to him, it is strange for me to relate to my family differently.
Family adoption, as well as kids being raised by various other family members, is not an uncommon phenomenon. Personally, I believe that these life is too complicated to make sweeping generalizations. Each set of circumstances is so different that it isn't possible to say which is better--family adoption or simply family caregivers. However, one thing that I do believe to be true is this: each person is entitled to define their family in their own way. Don't judge others family or their relationship simply because it is different from your own, or the way that you conceive of it.