VERIFIED:

A married couple with two NCL cruise vouchers can't use them at the same time.

This is yet another reason you should have your spouse listed at a different address than you in the TR system.

If they have the same address, NCL will not allow them to take a "free" cruise on the same ship as you. (That is, they can be your second guest, but they can't get a second room on their voucher or Seven Stars benefit.)

However, there is a small silver lining. If you want to COMBINE your benefits and get an upgraded room, you can call Teresita at NCL at (305) 436-4410 between 6am and 2:30pm PDT. Not sure how much they will upgrade you, I'm guessing not much. Maybe a balcony to a mini suite.