Many years ago, we used a very simple and inexpensive CCTV surveillance sytem for this type of application (to give an operator a view of a difficult to see process).
We went to the local Sam's club and bought a simple system for under $300 that would show up to four camera views on one screen. I think it came with two cameras, but was capable of selecting any one of four inputs, or all four in a split screen fashion.
Paul