How real it is?

There is a surface that displays the texture from the camera (called camera A). There are two cameras in the scene (1 and 2). When moving one (for example 1) camera, I change the position of camera A, thus I create the illusion of movement without being in other coordinates. (to implement this presence, one camera is easy to implement). But if use 2 cameras and they are in different positions the for each cameras need redraw on waiting lists, capture RT and render for one and then for the second. But then the question arises how to implement the possibility of obtaining the camera number, which is currently being processed?