Not sure if this is just a posting typo, but there seems to be a wrong place for quote here (should include format=NV12).
You might aso use HW decoder, but you would have to post available modes of your cameras with :
# This is for camera with V4L node /dev/video0
v4l2-ctl -d0 --list-formats-ext
Note that with Nano there may be some restrictions with USB bandwidth when using multiple devices, especially with MJPG cams, but I have no Nano and may not further help.