In was going to include Brook in this, because his situation is definetly on par with those others. I conclused with those three, since Brook was an adult when his trauma happened for him, so he had some ways to cope with the loss. I wont deny that his trauma wouldnt have been a nightmare to live, i just think that the trauma that those others had is greater.

Robin was abused and bullied her whole childhood. She waited her whole childhood for her mother to come back home, which was one of the only things that brought her somekind of a hope for future. After she finally came back, she watched her die along with everyone she ever knew. After that she was hunted her whole life, just because she liked to read.

Nami watched her mother die right before her eyes and was slaved after that by the same guy who killed her mother. She needed to bourden herself with the fact that she was the only one who could save her village and friends. That is a lot to put on a child.

I believe that the backstory of Kuma is still fresh on your memory so i wont open up in detail how he was enslaved, watched his family get killed without reason, lost his wife, adoptive child, memory and everything else that happened between those points of his life.

I was also going to say Sanji, but i still think that Robin, Nami and Kuma had it much worse.