Yes, they are biological brother and sister. We get asked that a lot. I'm always surprised, because I think they look so much alike. Also, they are inseperable.
One afternoon I came home from work without Daniel (who usually travels with me.) He had an after-school program or a playdate or something. Lily greeted me, then looked for Daniel and then FREAKED THE #@*$ OUT when she realized he wasn't there. So much so that we went to pick him up early.
I've read about other siblings adopted together being similarily attached to each other. It makes perfect sense to me. If you've lost every other family member and the only home you've ever known, you'd be pretty stuck on the one person who's still around.
Daniel and Lily are certainly each other's best friend. But they weren't always. During the first trip, when we first we met them in their care center in Addis Ababa, we had them bring the baby down from the nursery to the big kid playroom. All the children shouted to Daniel that his sister was there. They crowded around her, tickling her and calling her name. Her brother looked at her and shrugged, then went back to playing ball. Lily was also un-impressed with her big brother. On our trip home, in our first days together, they mostly ignored each other. I suppose the excitement of two new parents and a new home was enough distraction.
Then we took them to the pediatrician for the first time. Lily had to be strapped into that horrible board thing to have blood drawn. She screamed and screamed during her entire exam. Andrew was sitting with Daniel in the waiting room. The baby had some milk and fell asleep, exhausted from the ordeal of American style medical care. It was then that I saw Daniel's face. He had tears in his eyes, and his face stern and terrified, his eyes accusing me.
Daniel is here next to me as I write this. Lily is napping. Her brother flits from activity to activity, unable to really enjoy himself solo. At some point he asks if it is time for her to get up. (Good God, NO! Never wake a sleeping Lily!)
Before we child-proofed (ahem, Lily proofed) the doors, Lily loved to try to sneak into her brother's room in the mornings to wake him up. Now she just bangs on the door, calling his name.
These two. I hope they always can't wait for the other one to wake up.