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Rhodent
The vouchers are indeed for the named passengers booked to the value of their ticket, this is set out in the T&Cs and you can read up on this in the thread for using vouchers:
Book with confidence policy - FlyerTalk Forums
Rebooking with e-voucher - FlyerTalk Forums
There isn't a way around this which is easy, you can both independently utilise the voucher value, they don't have to be on the same trip, they can be separated.
There is a convoluted way around this for you to potentially get the money back in hard cash. What was the value of the two tickets ?