Vampires don't exist, so you can make whatever rules you want. If you don't believe me read Vampire Diaries, Vampire Academy and Interview with a Vampire. Also, you're judging the film on the basis of the trailer. I saw the entire film and it was great fun!

Besides the horrible dancing and singing I'm mostly upset that in the trailer they managed to go against two of the biggest Vampire rules: They have no reflection and you cannot take their picture. I bet they're eating garlic pasta at some point too…