Hi,
For further investigation, you can try to launch the cameras in single gst-launch-1.0 command like:
gst-launch-1.0 v4l2src device=/dev/video0 ! fakesink v4l2src device=/dev/video1 ! fakesink v4l2src device=/dev/video2 ! fakesink v4l2src device=/dev/video3 ! fakesink v4l2src device=/dev/video4 ! fakesink v4l2src device=/dev/video5 ! fakesink v4l2src device=/dev/video6 ! fakesink v4l2src device=/dev/video7 ! fakesink
To check if the cameras can be run well in gstreamer command. If it works, you can try to run multiple cv2.VideoCapture(GSTREAMER_COMMAND) like:
Issue with multi-camera gstreamer capture using OpenCV - #6 by DaneLLL