facetime with same apple id and on different devices
You can use the same apple id.  Just add unique special email addresses to your apple id.
This link explains it nicely.  http://ipad.about.com/od/iPad_Guide/ss/How-To-Use-FaceTime-On-The-iPad_2.htm

Do you want to place calls between two iDevices using the same Apple ID? By default, all devices connected to the same Apple ID utilize the primary email address associated with that Apple ID. This emails they'll all ring if a FaceTime call is placed to that email address. It also means you can't place a class between two devices, just as you can't use one home phone to place a call to your house and answer it with another phone. But luckily, Apple has provided a rather easy workaround for placing FaceTime calls on the same Apple ID.
To place a FaceTime call between two of your Apple devices, you will simply need to add a new email address to one of the devices. This will allow FaceTime to differentiate between the two and place a call to a specific device.