Why do all the characters have similar names?

Wuthering Heights was Emily Brontë’s only novel, so we cannot compare the literary devices in this novel to her other writings. However, giving her characters similar names was clearly an intentional and impactful device. In doing this, Brontë shows the complex nature of familial relationships, our tendencies to repeat the mistakes of those who came before us, and the opportunity we all have to make the choice to be different.
Catherine Earnshaw loves Heathcliff, but she marries Edgar Linton because she thinks it is the right thing to do. Heathcliff was adopted by the Earnshaw family and given the name of a deceased son, which represents his place in his new family. He is preferred by their father over his other son, Hindley. Heathcliff and Hindley Earnshaw (Catherine’s brother) have an intense sibling rivalry, leading to much strife within the family. Later, Hindley’s son, Hareton, is raised by Heathcliff. Catherine (Cathy) Linton is Catherine and Edgar’s daughter. Linton Heathcliff is the son of Heathcliff and Edgar Linton’s sister, Isabella, whom Heathcliff married to get revenge on Edgar for marrying Catherine. Heathcliff encourages a romance between Cathy and Linton to advance his revenge on Edgar and Cathy, whom he blames for Catherine’s death. Cathy marries Linton but eventually falls in love with Hareton. She is able to do what her mother could not: do what she wanted with her life and find happiness.

The fact that the mixed-up names of the first generation of characters and the second generation of characters are all so similar and confusing is a deliberate literary trick of Bronte's. The various Lintons and Earnshaws, as well as the confusing "H" names (Heathcliff, Hindley, and Hareton), are meant to show the exact parallels between the older generation and the younger. Will Cathy Linton make the same mistakes as her mother, Cathy Earnshaw? Will the marriage of Linton Heathcliff and Cathy Linton be as abusive as the marriage of Heathcliff and Isabella Linton? Will Hareton pay for the mistakes of his father Hindley? Will love or pain win out this time around? The questions are all emphasized through the parallel naming.