as far as I know, OpenCV’s VideoCapture with DSHOW backend only takes plain indices that change with device enumeration, but not device paths of any kind. that is one of its longstanding weaknesses.
if both cameras are attached, then I expect that both are actually addressable through VideoCapture, by index.
I am not familiar with pygrabber and its abilities. you showed that it only enumerates one of your devices, right? then that seems to be an issue with pygrabber. it appears to be abandoned. no commit in 6 years.