Thank you very much for your prompt response. After various trials and errors, using the information from the link you provided, I was able to display live images from two Theta V cameras on RViz in ROS2 using the following pipeline and OpenCV!
thetauvcsrc mode=2K ! queue ! h264parse ! nvv4l2decoder ! queue ! nvvidconv ! video/x-raw, format=BGRx ! videoconvert ! video/x-raw, format=BGR ! queue ! appsink