Julie Plec confirmed that Klaus is the origin of the bloodline Stefan, Damon, Caroline and Elena are from. It is possible to unlink a vampire from their bloodline using magic.
The complicated, romantic relationship between the cured vampire/human doppelgänger, Stefan Salvatore and his former sire, the cured vampire/witch doppelgänger, Katherine Pierce. Katherine fell in love with Stefan when she met him in Mystic Falls in 1864.
Before Tyler was resurrected as a werewolf, Klaus remained the only hybrid of his bloodline until Adyelya, who is of Klaus' blood, sired Katherine.
Elena Gilbert (Nina Dobrev) and Damon Salvatore (Ian Somerhalder) have a sire bond in season 4 of The Vampire Diaries, and it has been a point of contention ever since.
The sire line of a vampire goes back to the Original vampire. Katherine sired the Salvatores. Rose sired Katherine, Someone named Mary sired Rose, and Klaus Sired Mary. So Stefan and Damon are part of Klaus' sire line.
After Elena became a vampire, she became sired to Damon and they slept together.
The sire bond does not influence feelings, only actions. In My Brother's Keeper, and We'll Always Have Bourbon Street, it was revealed that Elena, as well as Charlotte were sired to Damon, as it was his blood that turned them.
It turns out that Lizzie became sire bonded to Hope after she drank the blood that Hope had donated to the Salvatore School's first aid kits, thinking the blood belonged to a random vampire.
Julie Plec confirmed that Klaus is the origin of the bloodline Stefan, Damon, Caroline and Elena are from. It is possible to unlink a vampire from their bloodline using magic. This was successfully performed on Klaus by Davina. For reasons unknown, Klaus never sired new vampires after his sireline was severed.
Elena Gilbert (3rd Petrova Doppelgänger): Elena was born on June 22, 1992, in New Orleans, Louisiana. She is the biological daughter of John Gilbert and Isobel Flemming, and was therefore a descendant of Katerina Petrova, to whom she bears a striking physical resemblance.
In the season four finale of The Vampire Diaries, Graduation, Katherine slept with Niklaus Mikaelson and conceived her daughter, Adyelya.
Elena is the the third and also the final descendant and doppelgänger of Amara, the originator of the Petrova doppelgänger bloodline. Elena's death and transition into a vampire ended the Petrova doppelgänger bloodline, as she has no descendants because she is unable to reproduce and have children.
Why wasn't Caroline sired to Damon??? It was his blood she had in her system when she turned... IIRC, sire bonds only occur if the new vampire had strong feelings as a human for the vampire that turned them.
Alexia was changed into a vampire by a man, who was revealed to be Niklaus Mikaelson, she met who asked her if she wanted to live forever so she could take care of her brother.
Henrik is the tribrid son of Niklaus Mikaelson and Hayley Marshall-Kenner. He is the twin brother of Hope Mikaelson and the paternal older half-brother of Octavia and Remus Mikaelson.
Through her mother's Labonair lineage, Hope is werewolf royalty.
Another red-headed witch, Hope is super powerful. While she's not extremely ginger, when the light hits, there's no doubt that this teen witch is a red head.
James Salvatore is the paternal half brother of Damon and Stefan Salvatore. As once said by Damon the family name had to go somewhere. Giuseppe Salvatore had illegitimate son with one of the maids, presumably after Lily had "died".
Lillian "Lily" Davina Gilbert-Salvatore is a main character in Legacies. She was a former major recurring character in the eighth season of The Vampire Diaries and The Originals before being promoted to a main character in the fifth season.
In the end, Enzo chooses Lily because he is falling in love with her. He drugs Caroline with vervain and takes her hostage for the Heretics, as an offering for the side of the Heretics. In Never Let Me Go, they don't interact until the end of the episode.
And yes, the show later confirmed that Damon and Elena have multiple children - Jenna, Sarah Lillian and a son, Grayson.
Also, in the books, Elena and Katherine were half sisters due to having the same mother (though Katherine suspected Elena was a possible descendant), but in the TV series, they are related by blood and Elena is her descendant.
Elena is rejecting vampire blood because when a vampire takes a cure his/her body is adjusted in such a way that it will not take vampire blood for it's whole life. Same case happened with Katherine otherwise she would have survived her ageing with the help of Stefan or Damon s blood and be a vampire again.