Thanks Marquise. We got back from our trip on Sunday, turned out to be no problem getting seats together for the Dubai-Melbourne leg as we checked in pretty early at Birmingham, so all was fine. I did think I'd managed to crack the Qantas seat allocation the day before we flew, but when it got to the payment bit it wouldn't accept it. I think it's a glitch that Emirates and Qantas need to sort out, as it's ridiculous not to be able to do this, especially as the Emirates online seat allocation is free.
I've flown from Australia to the UK and back quite recently on Emirates and was allocated seats ahead of time no problem, including the flights operated in conjunction with Qantas. Would definitely check again as it seems ridiculous you cannot confirm long haul seats together with any airline (esp if travelling with a child) and I haven't heard of this before with Qantas.
We're flying to Melbourne next week. The flights are from Emirates, and I've been able to allocate seats on all parts of the outward and return journey, apart from Dubai-Melbourne, which is an Emirates flight number but operated by Qantas. Emirates told me that I would have to contact Qantas about that flight, but Qantas say that we can't allocate seats until we check in at the airport.
Am now worried in case we don't get seats together (Dubai-Melbourne is 13 hours!) as have DD (3.11). Has anyone any experience of booking Emirates flights that are operated by Qantas? Have travelled many times to Melbourne, but have always gone with Emirates.