So you want to use your tablets as additional displays for your computer? Pixo can help. It is a magnetic tablet mount that lets you attach your iPad or other tablets to your computer. It is compatible with 7.9 to 12.9 inch devices. You can always use apps such as Duet Display to do more with your tablet.
To use this, simply place two metallic stickers on your iMac and one on your tablet. Pixo uses very strong magnets to attach to your computer but allows you to remove your tablet at any time. The Pixo mount is expected to ship in November.