Q: I have an iPad 2 and an iPhone both with the same Apple ID. If my son FaceTimes me, can I receive the call on both devices at the same time? I would be at work with my iPhone and my partner would be at home with my iPad.
A: FaceTime is only designed for two-party calls, not group calling, so there would not be any way for both devices to be on the call at the same time.
If you have two or more devices configured with the same Apple ID and email address or phone number for FaceTime, when a call comes in it will ring on all of your devices, and will continue ringing until answered or declined. The call will be answered from the first device that picks up the call and stop ringing on other devices. Similarly, if a FaceTime call is declined from one of your devices, it will effectively be declined and stop ringing on all of them.
There are third-party iOS apps and services that do provide group video calling, however, such as Google Hangouts and Fring, however all devices must be running the same app and each user has to sign up for their own individual account with the service.