If you want to share the ability for someone to add users, line up story prompts for Authors, and edit stories, there's a very easy way to do this. Just add that desired person as an "Editor". They will then have all of those rights, and more.

To find out more about an Editor, please see this article.

Here is how to add an Editor: at the top of the Friends and Family section, click the add user icon.  This brings up the Invite User dialog box. Enter the person's name and email address.  Select Editor from the role drop-down list.

Just click Send Invite and the invited Editor will receive an email inviting them to join in!