The Alchemyst: The Secrets of the Immortal Nicholas Flamel by Michael Scott (2007) Delacorte Press 

The first in a series of adventures.  Sophie and Josh, twins find themselves confronted by an unbelievable world of magic and monsters, starting in San Francisco.  Nicholas Flamel, mentioned in Harry Potter, is the main thread through which the stories pass.  He is the Alchemyst.  His wife, Perrenel is a sorceress.  They are immortal because Nicholas discovered the Philosopher’s stone and a codex of changing words that gives them a monthly formula.  They tell the twins that they are the Twins of legend who will save or destroy the world.  Another immortal, Dr. John Dee, is also after them, to use their powers to return the Dark Lords to power over the Earth.  Flamel tells them that their auras are pure gold and silver, and he hasn’t seen a set so powerful.  But their powers need to be awakened.  He connects with a vampire, Skathatch, the Warrior, who has trained heroes through the ages, to protect them and takes them to a shadow realm where Hekate guards Yggdrasil.  She, in her younger form, awakens the Wind magic power in Sophie.  But before she is even able to give rudimentary help to Sophie so she can handle the awakening, the shadow realm is attacked by Dee.  He kills Yggdrasil, which dooms the shadow realm and the two other realms attached to the tree.  Flamel barely gets the twins out to Earth before the realm collapses, stealing Dee’s car on the way.  They drive to Ojai, where they meet the Witch of Endor.  She passes her knowledge, accumulated over ten thousand years to Sophie.  Dee catches up and attacks.  The Witch, using a mirror, sends Flamel and the twins to Paris.