Sadly, this is pretty annoying to do with Blender. Not only do you not have the ability to define more than one active camera, you ALSO can’t set the active camera via the command line. The easiest way to handle this is to make 2 linked copies of your scene, and give each copy of a different active camera. You can switch scenes on the command line with the -S or --scene flag. (note the upper case on -S)
thanx ninja dude, can i give more then one line so it will render scene 1 and scene 2 after it ?
my aim is to leave my 3 cam project to render it self at the weekend.
Just type them all up into a text file, make it executable drag it to your terminal, and run it. Google “making a shell script” if you need more directions on that one. It’s a skill worth learning, comes in handy all the time for many things besides being a cheap and dirty way to queue renders.