Astra Pro NL - unique serial number to identify (OpenNI, CV2)

Hello guys,

I have 3 Astra Pro NL Cameras. I want to open every camera at the same time in a new window, where the title says which serial number the specific camera has.

I tried with python, but this does not work.

The operating system changes the usb index order every time by restart. And the order of cv2.VideoCapture(index) is not the same as the index of openni2.Device.open_all().
I get the unique serial number with str(devices[i].get_property(c_api.ONI_DEVICE_PROPERTY_SERIAL_NUMBER, (ctypes.c_char * 100)).value).

But as I said, it does not work.

Then I thought about searching for an attribute of each camera, which I can get with openni and also with cv2. Like width, height or framerate.
And then I thought about changing it for each camera, for example camera1 fps = 30, camera2 fps = 31 and so on, to identify which camera is shown in which opened window.
But with python statements, I cannot change these attributes.

So, my question: Does anyone now another solution, which works, in python?
OR: Does anyone know a solution in c++, c# or another programming language?

Thank you very much.