BNC cameras over CAT5 to powerline adapters then to DVR?
What you want to do will not work.  Here's why:

1) Your cameras are analog.  We know this because you mention BNC connectors and baluns.

2) Using CAT-5 cable for analog signals works quite well, provided you are able to convert the unbalanced signal from the BNC output of the camera to drive the twisted (balanced) pair in the CAT-5 cable.  Your baluns perform this very important function.

3) The Powerline Adapters work with standard Ethernet signals.  These are packet-based, fully digital signals.  The Powerline Adapter simply will not understand the analog signal from the camera.  Similarly, the DVR will not understand the digital signal coming out of the Powerline Adapter.

If you absolutely must Powerline Adapters to get the signals from the cameras to the DVR, you may be forced to replace the entire camera and DVR system with a modern IP-based system.  

A modern IP-based camera and DVR system uses standard Ethernet signals that are compatible with your Powerline Adapter.