What is Yuuki's relation to Kaname? In Vampire Knight, the familial relationship between Yuuki and Kaname is relatively confusing. Can someone explain it?
Kaname is the founder of the Kuran family, and he was reawakened by Rido Kuran. After being reawakened, he was raised as the son of Haruka and Juri, who are Yuuki's parents. To summarize, Kaname is Yuuki's ancestor, though he was raised (after being reawakened) as her brother.

Yuuki was also born to be Kaname's wife, following the Kuran tradition of pureblood siblings intermarrying. 

Cited from the Wikipedia article, which cites manga chapters.