Taking Jean's side

It is because Jeff will never forgive them for what happened to his sister….

If they would have supported Jean no matter what, she might not have faced these many problems and suffered. How can they be so irrational and blame her for their parent's death. 

But they let her suffer with Vanessa and Adam's cruelty. He still remember what Charles have said him….

The mental pressure and stress she faced in her childhood are the main reasons why Jean is suffering with intense migraine. 

Some or other how he neither despised them nor felt warm feelings for them. Unlike his sister, he don't have any memories with them to forget what they did and forgive them. But in the same time he don't want to be totally hostile with them. 

After all, they are still his grandparents and took care of Jean as 'some' of her lowest points. 

...

Outside the room….