Plot summary

Don (Robert De Niro) and Ellie (Diane Keaton) were a couple in New England, married for twenty years before they got divorced. They have three children from their marriage - Lyla (Katherine Heigl), Jared (Topher Grace), and Alejandro (Ben Barnes), who is adopted from Colombia.In preparation for Alejandro's wedding, Ellie shows up at Don's (and her old) house. She finds Bebe (Susan Sarandon), Don's girlfriend of eight years (and Ellie's former best friend), almost having sex, scaring Ellie. They make small talk, and he shows her to her room. Meanwhile, Alejandro and his fiance Missy (Amanda Seyfried) are in a meeting with Father Moinighan (Robin Williams), the priest who will be marrying them. It is revealed that Alejandro's biological mother Madonna (Patricia Rae) is going to be coming from Colombia to the wedding, which upsets Alejandro since he does not have a "traditional" family, and his Catholic mother would not approve of that or the fact that Don and Ellie had been divorced.Lyla, who reveals she is separated, goes to the hospital and sees her 29-year-old brother Jared, an obstetrician. Lyla is terrified of kids & passes out in the maternity ward. They talk and it is revealed that he is a virgin and is waiting for the "right one". It is also revealed that Lyla is having difficulty having kids. Back at home, Alejandro tells Ellie about his mother coming to the wedding. Explaining that since she is a devout Catholic and doesn't believe in divorce, Alejandro asks Ellie and Don to pretend to be married for the next three days. Hearing this, Bebe becomes upset and leaves the house, clearly upset at Don. Alejandro's mother arrives with his biological sister, Nuria (Ana Ayora). Later, Nuria flirts with Jared, and ends up swimming naked in the family's lake as he watches.That evening, the family goes out to dinner with Missy and her parents Muffin (Christine Ebersole) and Barry (David Rasche), with Bebe as their waitress, which surprises everyone. Meanwhile, Nuria starts touching Jared under the table. Ellie sees Nuria giving Jared a hand-job. She brings Nuria to the restroom for a chat, telling her that American women behave differently with men. When they arrive home, Jared tells Nuria he wants to have sex, as she had suggested earlier, but she now tells him no, asking him instead to do romantic things for her such as read her poetry. Don and Ellie, meanwhile, have sex after Ellie sleeps in Don's room.Ellie and Madonna go for a walk in the woods and talk. At the same time, Don and Lyla talk privately and Lyla reveals she is pregnant. On the wedding day, before the ceremony, Don tells Bebe he had sex with Ellie. Bebe says she forgives them but then punches him in the face. She also reveals that Ellie cheated on Don with Missy's father before Don cheated on her. Muffin says that she knows about Ellie and Barry, and tells them that she is bisexual, implying that she is interested in a sexual affair with both Bebe and Ellie. Meanwhile, Missy and Alejandro have decided to get married on the family dock to escape the crowd. The family runs after them and, after some of them fall into the lake, the couple are back to the wedding reception.During the reception, Jared goes upstairs to talk to Nuria, who says she has decided to no longer follow Ellie's advice (about not being so available sexually), and they sleep together. Back at the reception, Ellie and Bebe have made up. Don surprises Bebe by proposing to her, and they get married on the spot. Lyla's husband Andrew (Kyle Bornheimer) arrives at the wedding and, upon finding out that Lyla is pregnant, makes up with her. Alejandro's mother realizes she has been lied to about his family and he runs after her as she starts to leave. But she reveals that her own past was not as pure as he thought, that she too had lied to protect him, and she forgives him.It is revealed just before the credits that Lyla has a daughter called Jane because Don adds her name to their family tree saying both her grandmothers are crazy.