I would suggest you cable the composite video of each camera back to an electronic video selector board. You should be sure to use quality 75 ohm coax cable with decent connectors. RCA type plugs can be used but BNC connectors would be better.

On the selector board you should investigate the use of a cool chip from Philips. This chip is basically a 4x4 video cross point switch. The input side has four high bandwidth video amplifiers and the output side is buffered via a amplifier capable of driving a low ohm load. The figure below is a snippett of a schematic I did of a video mux box showing two of these chips. You will note that the chips are controlled via an I2C bus connection. The outputs can be disabled such that it is possible to parallel up channels of switch between various packages or outputs.



Do note as well that up to 8 of these parts can be used on any one I2C control bus due to the S0-S1-S2 slave address select inputs. It is also possible to use this chip to switch component video signals as well. For example if S-Video on 4-pin mini-din connectors is in use you can program a pair of channels through the switch in parallel to pass the two component signals. Similarly if RGB in use you can program 3 channels through the switch in parallel.

The figure below shows a block diagram of what is inside this chip.



A link to the PDF file data sheet is here: TDA8540 Data Sheet

Good Luck
Michael Karas