Phillip
They left a lot of the information out about Phillip that makes him understandable, if not likable.
Phillip thought of Joachim as a father and was devastated when he left. He blamed Sarah for this, as she let him go. He also blamed Sarah for Elizabeth's death, as she assured him she would not die.
He and Lizzy were abnormally close, only eleven months apart and he called her "his baby". They were the only children at the estate during the war and this made it hit harder.
He and William had a complex relationship. William was unable to get close to Phillip, who resented him and wished he were Joachim but was also just a small boy confronted with a man who, regardless of blood ties, was a stranger.