Kindle ebooks are encrypted with a key that is unique to the device. It is not an account-based key. So any kindle ebook file that has DRM that can be read on your iPad iOS Kindle app cannot be read by your MacBook MacOS Kindle app.
If you want to store your kindle ebooks in calibre and use calibre to send them to different devices (or read them using calibre's viewer) you'll need to remove the DRM.
http://apprenticealf.wordpress.com/ is your starting point for DRM removal. Note that detailed help with DRM removal isn't permitted on MobileRead.