Not quite sure I understand what you mean, do you mean you want to try and book your car hire with points/miles? Seeing as you won't have many posted (or any at all) by the time you land, this isn't a good idea. And it is a bad use of points/miles anyway.
I was more thinking whilst booking if we quote QF FFP in TAS we may get better discount than if doing the same with BA Exec
Err.. No. It will just combine your points. You will each need to be a FF member and put your own numbers down. Household Accounts are for BA only, QF doesn't have anything similar.
Assuming we go for BA...is it beneficial for us to open household account assuming? just wonder if for example we will move up in BA hierarchy quicker (bronze, silver) if we both put our miles together against one rather than two cards, so we can both access lounges or get better deals on hotels/ car hire? is it too good to be true and there is no way we can achieve that using those flights