Did you purchase all the books on the same Amazon account?
Okay, try this please.
Open the kindle program on your computer, enter your Amazon account info on the registration page, and then click “Register” button to register the device.
After the kindle screen is loaded, click the “Archived Items” Tab from the menu. Then all of your kindle books will display in the new list.
Now, you can select your books which you want to transfer from Amazon Store.
Click the book title to start transferring, after the books have been downloaded; click the book title to start reading.
Please let me know if this does not work for you, or if you need any other assistance.Please take a moment to rate my service positively.
Thank you very much!