Bohrs' family. Brutally raped to death and seemingly worse. All the while done shortly after their husband/father's death.... oh and on his grave no less.
Worst in what way? Most humiliating is probably (manga) Syura's, the most cruel is Bols' family, the most painful is... probably someone else, maybe Sheele, being dissolved/shredded to pieces (however it works) alive must have hurt :|