If you are happy to line up with the other sheep, you can stand one behind each other.
I don't think that they would appreciate it if 2 adults stood together, kids I guess will be ok, but not adults.
There is a line in the carpet, that you are supposed to stand behind till called.
NOTE: even if you stand one after the other, if the static officer decides, he/she can split you up, so that you go into different queue for immigration processing.
Have edited my post as you are dep Australia out of BNE, which might or might not as yet, have Smartgate for outgoing passengers.
QF15 from BNE to the US, I can't say, but when I did BNE to SYD on QF8, I found BNEi airport, much better than SYDi airport for Immigration and international preflight security.
More airy, SYDi airport is very hot, dry, claustrophobic. Larger number of people passing through I guess.