(note: to make things easier on myself, I used the descriptions listed on the Twilight Wikipedia page, and despite the often questionable reliability of Wikipedia I can assure you that these descriptions are all accurate enough...although you might want to hold off reading these if you want to read the novels, as they contain some spoilers)
The seven of them all live together under the guise as being an adoptive family with some biological connections; in reality, they are related only by their conditions.
- Dr. Carlisle Cullen: The adoptive father of the Cullen children and husband of Esme Cullen. Born in London as the son of a Anglican pastor, he is around 360 years old and works as a doctor in Forks. After becoming a vampire, he spent hundreds of years resisting the smell of blood so that he could become a doctor. He changed Edward, Esme, Rosalie, and Emmett into vampires to save their lives.
- Esme Cullen: Carlisle's wife, who was found by Carlisle and changed into a vampire after a failed suicide attempt following the death of her baby. She is the mother figure of the Cullen family, and has a strong ability to love passionately.
- Alice Cullen (real name: Mary Alice Brandon Cullen): One of Edward's adoptive sisters. She is described as "pixie-like", and her movement is noted to be very graceful. Her special ability is seeing the future as soon as someone makes the decision to head down that particular path. This ability is very useful, as it gives the family forewarning to any dangers. However, she cannot see the future if werewolves become involved (they are immune to her power for unknown reasons). She is married to Jasper Hale, who is her soul-mate, and she loves Bella as if she were her own sister.
- Jasper Hale: One of Edward's adoptive brothers, and Alice's husband and soul-mate. He can sense and influence the emotions of people around him. He has the most trouble with the Cullens' "vegetarian" lifestyle, since he and Alice are the newest members of the family, and before joining them he spent almost a century living off human blood. He became a vampire sometime during the American Civil War. He was initially involved in vampire wars, creating new vampires and forming them into armies, until he met Alice and became a part of the Cullen family.
- Rosalie Lillian Hale: Edward's adoptive sister, who is self-absorbed and described as being the most beautiful person in the world. At first, she appears to play an antagonistic role in the story. She became a vampire when Carlisle saved her life after several men, including her fiancé, beat and raped her, leaving her to die. She is the wife and soul-mate of Emmett Cullen. Rosalie dislikes Bella because of Bella's willingness to give up her humanity for an eternal life as a vampire.
- Emmett Cullen: Edward's adoptive brother, and Rosalie's husband and soul-mate. As a human, Emmett went hiking and ran into a large grizzly bear. Provoked, the grizzly attacked and nearly killed him before Rosalie, who was hunting, interceded. She saved him and then carried him 100 miles to Carlisle, in hopes of saving his life by turning him into a vampire. He is extremely muscular, with dark curly hair and dimples.