In this case I am talking about the 2nd leg of AUS-EUR trip
No good these days as the second leg of QF1 is only two man!
I believe EK run a system of operating crew and relief crew. If you're rostered as relief crew you're expected to turn up to work ready to sleep. You then hit the bunk at top of climb.
Correct although the augmenting crew has responsibility to oversee and participate in pre-flight planning and calculation of the TO figures. Ask the crew of EK407 on the 345 in ML