You should setup a NI-DAQmx Task using the DAQmx Create Task VI. Your task can contain multiple channels (multiple Create Virtual Channel VIs), each channel having its own range settings. You can use a single Create Virtual Channel VI with multiple channels as you are doing, but this will limit each channel to have the same ranges.
If you use the DAQ Assistant and select multiple channels, you could setup the different ranges per channels there too. And then you could also have the DAQ Assistant generate the code for you.
Hope this helps.
Jared A