Nick admires and truly likes Gatsby and that can appreciated in the novel. He feels that Gatsby deserves a funeral in which a lot of people should attend, that he deserves to be honored. He sees something in Gatsby that most people cannot see. They are good friends and Nick is loyal to Gatsby and that is why he assumes this responsibility.
Wolfsheim reacts in that way because he has already seen the death of many people in his work. Wolfsheim believes that involving his feelings now would be a problem for him. This could show some hypocrisy.
