Splitting Reward Flights

CS are correct, it has to be from 1 account. The only exception is if 1 of you is gold, then you're allowed to pool your miles.

What you could do is book 2 one ways, i.e. book outbound with your miles and book the return with your wifes. Or have 2 separate return bookings, one for you and one for your wife.

Normally you can use miles from another account to pay for an entire sector (not the same as pooling) but it may be that trying to use a companion voucher prevents that from happening.