Call Customer care and ask them to cancel just one add-on card. If asked, mention that you wanna apply for a different family member. Once the call is done, login to netbanking and apply for a new add-on for your wife. It should get delivered in about 3 days with a new card number and linked...
The limits are at a mobile number as well as a credit card irrespective of primary or addon.
Eg. - I have 3 cards. MRCC, PT and Gold addon. Across these 3 for my number, I can buy Max 25k Apay. Let's MRCC 6k, Gold 6k & remaining 13k on PT.
I can use another number and buy remaining 12k on PT.