[Lockwood:] I began to feel unmistakably out of place in that pleasant family circle. (2.63)
No matter how insightful he believes he is, Lockwood ultimately remains an outsider to the scene he describes. Nonetheless, he believes he has a chance with the young Catherine. The question is: knowing what he knows, why would be want to marry into this family? What does that tell us about him as a narrator?
The ledge, where I placed my candle, had a few mildewed books piled up in one corner; and it was covered with writing scratched on the paint. This writing, however, was nothing but a name repeated in all kinds of characters, large and small—Catherine Earnshaw, here and there varied to Catherine Heathcliff, and then again to Catherine Linton. (3.7)
Catherine's entire story is cryptically recorded on the ledge of her bed. She will become Catherine Linton, as she fantasizes about as a young girl, but it is her daughter who becomes Catherine Heathcliff.
"I see the house at Wuthering Heights has 'Earnshaw' carved over the front door. Are they an old family?"
"Very old, sir; and Hareton is the last of them, as our Miss Cathy is of us—I mean, of the Lintons." (4.27)
What becomes of these two family lines is one of the main concerns of the novel. As Nelly explains this piece of family history, she lets it slip how much she sees herself as one of the Lintons. This suggests that there may be some bias in her narrative.
They entirely refused to have it in bed with them, or even in their room; and I had no more sense, so I put it on the landing of the stairs, hoping it might he gone on the morrow. By chance, or else attracted by hearing his voice, it crept to Mr. Earnshaw's door, and there he found it on quitting his chamber. This was Heathcliff's first introduction to the family. (4.50)
Our "trusty" narrator, Nelly, participated in the Earnshaw family's rejection of the young foundling Heathcliff. Again, Nelly reveals little clues about the kind of narrator she is and how she may be more sympathetic to the Lintons.
"Tell us where you got your lessons, and you shall have it," said I.
"Who's your master?"
"Devil daddy," was his answer. (11.18-19)
Hindley is too much of a mess to even treat his own son with any decency. Between Hindley and Heathcliff, Hareton is raised like an abused animal, so the fact that he grows up to be decent is truly surprising.
And from what I heard, Joseph contributed much to his deterioration, by a narrow-minded partiality which prompted him to flatter and pet [Hareton], as a boy, because he was the head of the old family. (18.78)
Though in the background, Joseph has his own role in perpetuating the drama. So it's not only Heathcliff and Hindley doing a poor job of raising Hareton—Joseph, a fairly minor character, plays a role too.
Catherine Linton Heathcliff
"Oh, Ellen! don't let them say such things," she pursued in great trouble. "Papa is gone to fetch my cousin from London: my cousin is a gentleman's son. That my—" she stopped, and wept outright; upset at the bare notion of relationship with such a clown. (18.72)
Upon first meeting her cousin, young Cathy allows status anxiety to guide her treatment of Hareton. Like her mother, Cathy wants to belong to the right people. What she doesn't realize yet is that Hareton is in fact the rightful owner of Wuthering Heights.
My son is prospective owner of your place, and I should not wish him to die till I was certain of being his successor. Besides, he's mine, and I want the triumph of seeing my descendant fairly lord of their estates; my child hiring their children to till their fathers' lands for wages. That is the sole consideration which can make me endure the whelp: I despise him for himself, and hate him for the memories he revives! (20.43)
Linton Heathcliff is merely a pawn in his father's grand scheme for revenge. Like the two houses that Heathcliff covets, Linton is a piece of property.
Ellen "Nelly" Dean
"These things happened last winter, sir," said Mrs. Dean; "hardly more than a year ago. Last winter, I did not think, at another twelve months' end, I should be amusing a stranger to the family with relating them! Yet, who knows how long you'll be a stranger?" (25.1)
Nelly indulges Lockwood's fantasy that he actually has a chance with Cathy Heathcliff. Why she does this is unclear. What's even stranger is that Nelly would think that this union would be a good idea. These people don't seem to marry outside the family.
I shall be your father, to-morrow—all the father you'll have in a few days—and you shall have plenty of that. (27.61)
Heathcliff's promise of fatherhood spells misery and certain abuse for his soon-to-be daughter-in-law. Here, as elsewhere in the novel, family roles are very confused. Heathcliff was a brother but never really treated like one—nor acted like one. Now he will be a "father" who acts like no father should.