How does one upload an Amazon.com-purchased digital book to a "Third Kindle" which is part of a different Family Member's Account (three of us share the same library)? I purchased a Kindle book from Amazon.com thinking it would automatically upload into my Kindle cloud, shared with other family members, but it didn't because it's not my own account. And, now it's too late to cancel the book order (just joined Prime and saw a digital book deal too good to pass up when I purchased from the website). Do I just need the main account holder's Kindle account number to input somewhere, or that plus other identifying info.? Many thanks for any help.