Write down all of the details that you can think of. What did you see? What did you hear? What did you smell? What did you think about? Where were you? Etc.
Then draw up an outline of how you think the story will progress, change the outline as you need to to make your story work.
Then just start writing the first sentence.
Take into mind whether you want your story to start with your present life, or with one of the other lives, and whether you want to jump back and forth in time.
Find a competent and knowledgeable person who can edit, regularly for you, to make sure everything is consistent and correct grammatically.
Sounds like a pretty interesting concept for a novel if you ask me : )