The phrase "You kill" expresses how badly the people behave in order to get what they want. It can be translated as "You do all kinds of evil things to get what you cannot have" (See: [[rc://en/ta/man/jit/figs-hyperbole]])
The words "fight" and "quarrel" mean basically the same thing. James uses them to emphasize how much the people argue among themselves. Alternate translation: "You constantly fight" (See: [[rc://en/ta/man/jit/figs-doublet]])