It is supposed that the school was founded by the "Holy Order" to give shelter to the orphan teenagers...who happen to be vampires, werewolves, hunters, etc.
So most of the parents of the characters are dead, or left them when they were quite young.
I know this is not quite logic...but I thought it would be a nice idea.
The Holy Order is a school managed by priests of all around the world and all the religions.
All the cast of the film is going to appear, but they are around 16, 17 years.
I don't own Van Helsing or related ( ::looks at Dracula and cries:: )