Yes, you can have multiple Kindle Direct Publishing accounts. You will need to create a new account for each book you want to publish.
You affirm that you are at least 18 years old (or the age of majority where you reside if that is an older age) and capable of forming a legally enforceable contract. A parent or guardian can establish a KDP account on behalf of their child and become the minor’s Book’s Publisher.
You can list authors in the Contributors area if you have more than one. Simply pick “Author” from the dropdown menu of contributor kinds. On the detail page, the name listed in the Author column will be displayed first.
You get a 35 percent royalty on every sale for ebooks priced between $0.99 and $2.98, and a 70% royalty on each sale for titles costing more than $2.99. For books priced between $2.99 and $9.99, you receive a 70% royalty on each transaction; you receive a 35
