Rabbi Sendak's name is a reference to Maurice Sendak, writer of children's horror classic "Where the Wild Things Are".
Rabbi Sendak has a sign in his office that reads "When God made Man, She was Only Joking!"
The doctor that Sofia is talking about as she recounts her time in Auschwitz is the infamous Dr. Josef Mengele. He was notorious for selecting those that came off the cattle carts for those who lived or were sent to the gas chambers. He was particularly interested in experimenting with people, whether it be freezing people in sub-zero water or changing the color of the iris of eyes. He also had a deep interest in twins and would do organ switching, blood transfusions or sewing twins together.