Hi,
The sample config file for single USB camera is
/opt/nvidia/deepstream/deepstream-5.1/samples/configs/deepstream-appsource1_usb_dec_infer_resnet_int8.txt
Yo may try to run it and then modify config fie to run multiple-USB-camera case. Here is a config file for 4 USB cameras:
DeepStream4 Jetson nano multiple webcams issue - #12 by DaneLLL