Find That Book

I'm trying to find a book I read around 7 to 8 years ago. I can't remember a lot about it, but the main protagonist was an orphan boy. The orphanage was kind of strange and creepy because it would be visited by these bird men or something. It's possible they were also the ones who brought the boy, I can't remember. I also can't remember what made him want to leave, but he eventually runs away from the orphanage with another boy and girl who I think were both mean to him. Again, I don't remember anything that happens until around the end of the book. There is an adult couple who convince them that they are two of the children's parents. I remember this one specific part regarding the girl: she asked the lady to brush her hair because she thought it was a mother-daughter thing (actually now I'm not sure if she asked the fake lady or her real mother later). They eventually find out these people are lying to them to harm or kill them, and they also find their real parents and I think it turns out that all three of them are actually siblings and they are all royalty. I also think the main protag kills a dragon at some point. I hope someone can identify this book!!