Mr. Heathcliff, the landlord of Wuthering Heights in the opening scenes of the book, was an orphan, found on the streets of Liverpool by "The Old Master" [Old Mr. Earnshaw] on a long trip on foot.  Heathcliff, whose name was both first and last name to him, was adopted, but it seems not formally, to be a brother to Hindley and Catherine.  Heathcliff had been the name of a stillborn child of the Old Master and his wife

Hindley Earnshaw was married to a girl who was barely described; their child was Hareton Earnshaw, the surly youth.  Ellen cared for him as a baby.  He was basically illiterate.  His mother died in childbirth

Isabella Linton, Mr. Heathcliff's wife, was one year younger than Catherine Earnshaw Linton.

Heathcliff had always loved Catherine Earnshaw "senior" and made his marriages primarily out of revenge and cruelty.

Heathcliff married Catherine E. Linton's sister in law Isabella Linton, and their child Linton Heathcliff was born at their home in London.

When Linton Heathcliff was 12 years old, his mother Isabella died, thus setting Mr. Heathcliff free. . . .

"Cathy" Linton, the child of Edgar Linton and Catherine Earnshaw Linton, was also cared for in infancy by Ellen.

Linton Heathcliff, who was always a sickly child, and proud, was growing up at Wuthering Heights, and his cousin Cathy Linton fell in love with him, and they got married--as was prearranged--willingly, though Linton H. died very soon after.

At the near-end of the story, close to the "present day" of the narration, Catherine E Linton, widowed, died, wasted away; Hindley Earnshaw, her brother, died six months later.

As the story is near completion, Cathy (junior) is planning to marry the lout, Hareton Earnshaw.  It seems as if the author wants us to approve of the match though Hareton has always seemed a lowlife in the previous parts of the book.