Last Thursday, TVD revealed that Jo is Kai's sister and that she was one of the family members he tried to kill when he went nuts a massacred his coven. During this week's episode, "Fade Into You," TVD revealed that Liv and Luke are related to Jo and Kai.

Who is Jo's twin brother?

Chris Wood - Kai Parker (Dr. Jo's twin brother - witch) | Chris wood, Chris wood vampire diaries, Christopher wood.

Who is Kai's sister?

Josette Laughlin: Kai's twin sister who, unlike her brother, was a witch.