بسم الله الرحمن الرحيم
(Fatwa: 739/703/M=6/1438)
In the question mentioned above, you may pay the zakah of your wife to your sister with her permission provided she is poor and eligible to receive zakah. If your sister has become sahib-e-nisab due to jewelry etc then it is not correct to give her zakah.
Allah knows Best!
Darul Ifta,
Darul Uloom Deoband
