Thanks markis10.
I also called Qantas, and they said 1 room - although the agent seemed to be reading from a sheet that said "up to 4 adults per room", so not sure if she is confident with her answer - and given Dubai laws regarding marital status, that must mean "2 married adults + their 2 adult children"!
Not too fussed, since we would unlikely stay there for much more than 4 or 5 hours. Just after all the facts so we can choose between VCE-DXB+9 hour DubaiConnect transit or VCE-MXP (3.5hr drive) + MXP-DXB+3 hour transit.