How the Deepstream can support the multiple Videos input which from Multiple USB cameras and to do the analysis

Before customizing deepstream-test1-usbcam, we suggest have a working gst-launch-1.0 command for MJPEG decoding, so that you can do customization based on the command. For launching USB cameras, please refer to
Jetson Nano FAQ
[Q: I have a USB camera. How can I launch it on Jetson Nano?]

You would need to configure exact format/width/height/framerate of the v4l2 source(USB camera)