Mary, the eldest Crawley sister, is initially betrothed to her cousin Patrick, since she is not allowed to inherit her father's estate and title in her own right. After he dies along with his father on the Titanic, she refuses to even consider the same arrangement with the new heir, Matthew. Over time, however, the two fall in love and, after quite a few ups and downs, marry. Tragically, Matthew is killed in a car crash on the same day that Mary gives birth to their son and heir, George, who is now next in line for the earldom. Years later, Mary remarries to Henry Talbot, a race-car driver and businessman. They have a daughter, Caroline, and they spend more time apart than they'd like due to Henry's work travel.
Edith, the middle daughter, goes through the wringer emotionally for much of the story. Her first engagement, to the much-older Sir Anthony Strallan, ends when he leaves her at the altar. She next falls in love with Michael Gregson, her editor at the newspaper where she writes a column, but he reveals that he is technically still married to his first wife, whose mental incapacity means he cannot get a divorce. He plans to go to Germany and get citizenship there so that he can get a divorce and marry Edith. They spend one night together before he leaves, resulting in a daughter, Marigold, before Michael is tragically killed in a failed Nazi coup. Edith struggles to find a way to keep her daughter in her life, eventually crafting a story to allow the family to take in Marigold as a "ward." Eventually, she falls in love with Bertie Pelham, a land agent and a cousin of the marquess of Hexham. When Bertie's cousin unexpectedly dies, Bertie inherits the marquessate. Although Bertie initially balks after learning the truth about Marigold, he apologizes to Edith and proposes. They marry, making Edith the marchioness of Hexham, and they eventually have a son, Peter.
Sybil is the youngest and most rebellious of the Crawley sisters. She befriends Tom Branson, the chauffeur at Downton, over their shared progressive politics. Over the years, their friendship turns romantic, and she goes against her family to marry him and leave for Ireland. They return to Downton while Sybil is pregnant with their first child, but Sybil dies from pre-eclampsia shortly after giving birth to their daughter, Sybbie. Tom spends the next several years as a widower, although he does slowly become a true part of the Crawley family. He, too, finds love again in the end, falling for Lucy Smith, the secret daughter (and heiress) of one of Robert's cousins.
