what roles do the personalities of the narrators play in the way that the story is told?

There are really two main narrators: Lockwood and Ellen "Nelly" Dean. Ellen Dean has been a servant with the Earnshaws and the Lintons for all her life, and knows them better than anyone else. She is independent and high-spirited, and retains an objective viewpoint on those she serves. She is called Nelly by those who are on the most egalitarian terms with her: Mr. Earnshaw, the older Catherine, and Heathcliff. Lockwood is a gentleman from London, in distinct contrast to the other rural characters. He is not particularly sympathetic and tends to patronize his subjects.