"What were your brother's real parents like?"
The above question is one that will trigger an impulsive desire for me to call the inquirer an absolute idiot.
I am the big sister of five fantastic young men, two of whom are adopted. The younger of the two, who was adopted fifteen years ago by my mother and father, never knew his biological parents as his parents. He was two months old when he came to us and he has been my little brother ever since that day. The same mother who carried and gave birth to me baked his first birthday cake, arranged for his first haircut, bandaged his first scraped knee, and has taken pictures of him in all his numerous accomplishments over the years. The same father who sang me to sleep when I was an infant is the same father who played peek-a-boo with my brother, cheered him on at football games, disciplined him when he needed it, and ultimately was his first real broken heart when we had to lay Dad to rest.
The older of my two adopted brothers has just recently joined our family, but that doesn't make him any less my brother. My mother and stepfather love him just like they love the rest of us. While there is a lot of his life we missed out on, my mother has the same expectations and hopes for him as she does with any of the rest of us. She didn't carry him in her womb, and she didn't even see his first day of kindergarten or his gap-toothed smile in grade school. My stepdad wasn't there for his first steps or his first fight. However, they are now getting to be the parents he comes home to when he makes an awesome play in football practice or when he's given an extra heavy homework load. They look at him and see how great a person he is and they are thankful they get to be his parents for the rest of his life.
I say all this to say that my brothers and I are the same in our parents' eyes. Likewise, our parents are the same to all six of us kids. Asking about an adopted child's "real" parents implies that an adoptive family isn't real. It dismisses all of the hours adoptive parents spend worrying about, caring for, and loving their children. It implies that the love an adoptive parent gives their child isn't quite good enough to be "real." Quite frankly, it's just plain rude.
Do the world a favor: don't ever ask about an adopted kid's "real" parents or family. If you're curious, ask about their biological family. Ask how comfortable they are talking about their familial history. Please, never imply that the people they call their parents aren't their "real" parents.