How does the ghost suffer in Oscar Wilde's story "The Canterville Ghost" and who helps him in his redemption?

The ghost of Sir Simon suffered mostly at the hands of the Otis twins, and Virginia Otis helped him earn his redemption. 

The entire Otis family, with the exception of Virginia, antagonizes Sir Simon during the story, but it is the twins who really give the ghost a difficult time.  The two youngsters pull just about every summer camp prank that they can think of on Sir Simon.  They put a bucket of water up on a door to soak the ghost as he comes through it.  They pull string across hallways to trip the ghost.  They shoot peas at Sir Simon with their pea shooters.  They even put melted butter on the floor to make it slippery enough for Sir Simon to fall.  

Virginia helps Sir Simon by being sympathetic to his plight.  She listens to him confess his wrongs, and she prays for him upon his request.  Because of Virginia's actions, Sir Simon is finally able to find eternal rest.