Thanks for the reply...some answers:
1. No Siamese cable
2. I believe the power supply is 12V box
3. Not sure what power connectors are on the cameras, they are older RCA's. I would have to take one out of an elevator and check. I can only see 2 cables, 1 red and 1 black and they are terminated into the camera.
4. BNC is crimped
We would like to replace the whole system, the cameras are old, black and white screens, and the multiplexer seems to go down periodically (panasonic wj-fs216).