I came into it late

http://en.wikipedia.org/wiki/The_Quiet

Dot (Camilla Belle) is a young, orphaned, deaf and mute teenager. After the death of her also deaf father, she is sent to live with her godparents and their daughter Nina (Elisha Cuthbert), with whom she used to be close friends. However, she soon learns the secrets her new family withhold from the rest of the world as well as from one another.

Creepy and biological. Ayup.