If each camera has it's own unique internal IP address, then you should be able to view them simultaneously by running one instance of iCamSources for each camera. You'll need to enter each camera's MJPEG URL into a separate instance iCamSource.
If the MJPEG or JPEG URL isn't something that can be found by searching around with Google or by contacting the manufacturer's support, we actually have another solution available, although it is currently in its very preliminary stages, and that is:
http://skjm.com/icam/mjpeg_test.phpWhen you enter the camera's IP address and port into that web page, it will attempt to connect to the camera using all of the common MJPEG and JPEG URLs that we are aware of. If any of the URLs produce an image, then that is the URL to use in iCamSource.
If your camera requires a login and password, you can enter them in that webpage right before the address : login:password@Camera_address