Don't stress about this. It sounds like a note has already been made in your booking that you and your husband want to sit together. Qantas should pick this up when it looks at seating for the flight before check-in opens and starts to make arrangements and adjustments. You may well find that it has been sorted out by the time you reach check-in.

If it hasn't, ask the check-in agent to try to sort something out. Even if they can't do it there and then, it may get done between check-in and boarding. (For example, someone who is being involuntarily upgraded from economy may get their seat changed before they have been told about their upgrade.) If you use the business class lounge, you may get told what's happening while you're waiting there.

Asking on-board is a last resort if all else has failed up until that point.

You might also want to ask the experts on the Qantas board who have more intimate knowledge of how QF's seating works.