Because there twins and are dating the others.
His sisters are Alice Cullen and Rosalie Hale. there real names are: Alice Cullen is Ashley greene rosalie hale is:Nikki reed His brothers are Jasper Hale and Emmett Cullen. jasper hale is: Jackson rathbone emmet Cullen is: kellan lutz Rosalie was too smug to get rid of her old last name so she kept it and jasper's last name got changed to Hale too because Rosalie and Jasper could pass off as twins and it would also help the Cullen's story.
carlisle Cullen,Esme Cullen,emmet Cullen,Edward Cullen,rosalie Cullen,jasper Cullen and Alice Cullen
Esme Cullen, Carisle Cullen, Edward Cullen, Emmett Cullen, Alice Cullen, Rosalie Hale, and Jasper Hale.
Wow, who ever put that thing was WRONG!Gah, stupid people.Emmett: Emmett Dale McCartyRosalie: Rosalie Lillian HaleOkay, we all know their names now:Emmett is: Emmett Cullen.Rosalie is: Rosalie Hale.
They already had last names for when they were changed to vampires so they didn't change there names for when they became apart of the Cullen family
carlisle alice rosalie emmett esme edward jasper
Edward and Bella, Alice and jasper,rosalie and emment and carlisle and Esme
Carlisle, Esme, Alice, Edward, Jasper, Rosalie, and Emmett.
Carlisle Cullen Esme Cullen Alice Cullen Jasper hale Cullen Rosalie hale Cullen Emmett mason Cullen edward Anthony mason Cullen Isabella Mary swan and soon to be Isabella Mary Cullen Reneesme carlie Cullen.
Carlisle Cullen, Esme Cullen, Edward Cullen, Alice Cullen, Jasper Hale, Emmett Cullen, and Rosalie Hale. In Breaking Dawn, Bella and Renesmee Cullen join the Olympic coven.
Carlisle Cullen - Carlisle Cullen Esme Cullen - Esme Platt (after marriage: Esme Evenson) Rosalie Hale - Rosalie Lillian Hale Emmett Cullen - Emmett McCarty Alice Cullen - Mary Alice Brandon Jasper Hale - Jasper Whitlock Edward Cullen - Edward Anthony Masen
Excluding the names mentioned in the question. There other Cullen's are: Carlisle Esme Rosalie Emmett