micro camera

If you can't find a slim camera for the corners, maybe consider this unconventional "out of box" idea,  Mount the two cameras under the layout then drill holes so that cameras can see small mirrors that reflect images.  Might need to play with images as far as reversal and orientation so things are right side up.

Worth a shot.

Maybe the camera from Lionel camera cars? Parts here. 

After looking into it a bit something like this from Arducam would work well. Plug and play usb and with a free security camera software program you can view both cameras on a laptop simultaneously. So far in researching this stuff there seems to be a field of view (FOV) limitation with the camera that can also focus in on objects that are closer. If you want a FOV that is 90 degrees or above, which is preferable for a corner location in the roundhouse to view all the engine stalls, the focus is limited to objects 1 meter and out. They have a camera that will do a 76 degree FOV and focus on objects just a few inches away.