Omg nobody has answered you
1. Neji and Hinata are cousins. Some claim that Hiashi and Hizashi are identical twins so they might be genetically half-siblings. But in my opinion Hiashi and Hizashi do look similar - but not identical.
(Though I also saw at first sight that the Neji clone was not Neji too...)
2. Canon - I think most would describe it as crack, since the ending *pukes* indicates other pairings.
In a way it i to s not totally cracked up though. Neji's death could be viewed as sacrifice for his love. His speech in the manga (in the anime it is totally different) could also be seen as some kind of hidden confession, if you ask me. (People were just too much after NaruHinasee it.
So, in some ways it is canon, in some ways it is still crack ;D