It might be easier connecting all the cameras to an unmanaged switch that is then connected to either LAN 2 or 3 of the SX80, while you have the camera's video go into an external video switch that outputs to the camera 1 input on SX80. For camera control, you'll use your control processor to control the cameras through the codecs API using xCommand Camera PositionSet or Ramp.
Note, this is untested, but a working theory.