Is it possible to have the same apps from the same amazon account on 2 different devices? My kids have an android tablet each both linked to my amazon account. When I try to put the same app on both it tells me it's not possible.

How can this be fixed?
Did you register the devices with Amazon?  You can install amazon store purchases on multiple devices, but they must be authorized.  When you are in the app store, looking at an app, there should be a list of your devices, under the purchase button, with a notation on which devices the app will work with.