Originally Posted by
MSPeconomist
Once you do the switch, that person stays in the coach cabin for the entire flight. No switching back and forth or visiting.
That's the correct advice, and JNB would not allow more back and forth because of length, it is just a standard flight (I think the only potential exception would be LHR-SYD whereby crew might accept that people change at SIN).
So let crew know from the start that Miss x will be in seat xxx and Mr y (I assume he won't let you sacrifice yourself!) will be in seat yyy instead of the other way round.