Olive is a Mexican American woman with a biology PhD who recently lost her job in the pharmaceutical industry. She considers herself a perpetual pessimist cursed with bad luck since a childhood incident involving a stuffed animal arcade game. Despite her career setbacks and self-doubt, she is fiercely loyal to her large extended family and maintains a sharp wit. She strongly dislikes her new brother-in-law's sibling, Ethan, viewing him as judgmental and critical.

Ethan is Dane's older brother, working on the statistical side of digital advertising. He is a serious, analytical man who refuses to eat from buffets out of concern for food safety. This strict habit saves him from the food poisoning incident at his brother's wedding. He frequently trades insults and banter with Olive, though his demanding exterior hides a fear of flying and insecurities stemming from a recent breakup.

Ami is Olive's identical twin sister and works as a hematology nurse. She is an extreme optimist with a talent for winning contests, which allows her to finance most of her lavish, Christmas-themed January wedding through various prizes. Highly organized and confident, she insists that Olive take her nonrefundable honeymoon trip to Hawaii after severe food poisoning ruins her reception.

Dane is Ethan's younger brother and Ami's new husband. He has a dudebro personality and a crude sense of humor, often planning adventure trips around holidays. Olive strongly dislikes him, sensing that he is thoughtless toward her sister. Ethan defends his character fiercely out of family loyalty.

Sophie is Ethan's ex-girlfriend who happens to be vacationing at the same Hawaiian resort. She is a cheerful, extroverted, and conflict-averse woman whose sudden departure from Ethan's life six months prior left him deeply wounded. Her unexpected presence prompts Ethan to pretend that he and Olive are a happily married couple.

Mr. Hamilton is the head of Hamilton Biosciences, a pharmaceutical company that recently offered Olive her dream job. He is vacationing in Hawaii with his wife for their anniversary. He strictly values personal integrity and honesty in his employees, making Olive anxious about hiding the true nature of her trip from him.

Molly is Mr. Hamilton's wife, celebrating her wedding anniversary in Hawaii. She is friendly and eager to invite Ethan and Olive to social events for company employees. She wholly believes their cover story about being newlyweds.

Billy is Sophie's new fiancé. He makes awkward conversation with Ethan and Olive during a boat excursion. He has a crude sense of humor regarding Olive and her twin sister.

David is one of Olive and Ami's nineteen cousins. He owns Camellia, a high-end restaurant in the Twin Cities. He provides immediate support and employment for his family members when they face professional setbacks.

Natalia is another of Olive's cousins who frequently checks in on her. She acts as a conduit for family news, keeping Olive updated on Ami's well-being. She is highly supportive of her cousins during difficult times.

Trinity is an acquaintance of Dane from the period when he was first dating Ami. Her past connection with Dane becomes a subject of interest to Ami and Olive.

Olive and Ami's mother is described by Olive as resembling Joan Crawford. She is estranged from their father but remains legally married to him. She offers blunt, bilingual commentary on her daughters' appearances on the morning of the wedding.