Hi Ankita,
you cannot maintain multiple number ranges for one backend system, and I am afraid that only one of them can be set as internal or external number range. Our system only allow one internal number range and one external number.
This is sensible, because system has to find out the right number range to determine the document number.
You may also refer to trx BUC2 which will define internal and external number ranges for business partner and only one selection is allowed.
Best regards,
Ivy