Quote - Perhaps I am misunderstanding the problem

Yes you are. The objective is to have a pair of cameras in lock step, but only have to set the animations of the first one - the second is attached and automatic.

Your suggestion is to re-keyframe for the second camera, as if its movements are independent.

Parenting the second camera means that it will exactly do what the OP asked. And parenting is not gobbledygook. If I explained the math of parenting, which is actually required to make clear why William's suggestion is wrong, then it would be goggledygook.

William - when the viewpoint is turned, the displacement is no longer on the x axis. For the second camera to be 6 inches to the right of the first camera at all times, means that you move the second camera with respect to the first camera, not with respect to the world axes. In particular, when the cameras turn 180 degrees, the translation is in the exact opposite direction. When the camera turns 90 degrees, the translation is completely in the Z axis, and not at all in the X axis. When the camera tilts and rotates (as would be the case when shooting from an airplane's point of view), the translation would be non-zero in all three axes.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)