The Draco Trilogy/WMG

The Draco Trilogy is set in an Alternate Timeline.

The point of divergence is Dumbledore and Fudge's parting of the ways at the end of Harry Potter and the Goblet of Fire. In the Draco Verse, Fudge accepted Voldemort's return right away, causing the following changes:

Fudge remained in office past Harry's fifth year.
With the Ministry taking Voldemort's return seriously, Dumbledore never felt the need to reform the Order. Harry never went to Grimmauld Place, instead spending that summer at Hermione's.
Fudge insisted that Snape work for the Ministry due to his experience in dealing with Voldemort, so he never became a spy for Dumbledore.
Since Umbridge was not sent to Hogwarts, Dumbledore's Army wasn't formed, meaning Luna never got to spend enough time around the principal characters to become important.
Voldemort didn't bust his followers out of Azkaban in Harry's fifth year because the Ministry was more prepared.
Harry was able to go to Dumbledore when he saw the vision of Sirius in the Department of Mysteries. Therefore, the battle in the Department of Mysteries never happened, including Sirius' death and Lucius' capture.
Without all the drama of Umbridge's takeover, Blaise Zabini had lots of time for soul searching. Thus, he realized that he was a girl living in a boy's body and had a sex-change operation.
As for Sirius and Narcissa... well, they really are cousins. They just lie about it to stop people from getting Squicked by their incestuous relationship. They can get away with this because Harry never saw the Black family tree.
- The lying is unlikely, simply because the notion of cousins in a romantic or sexual relationship doesn't upset people in the U.K. Americans are the ones who tend to be horrified by the concept. This may be because wealthy and powerful European gentry, nobles and royals have married cousins for centuries, whereas Americans typically associate cousin marriage with the inbred and ignorant rural poor.