having used QF award booking to also secure the economy seat, is there any way to upgrade to J at least with points or cash if it’s available?
I think the only option would be to cancel the Y and rebook in J/F if available.
As these flights have a four hour stopover in Dubai and I have access to first class lounge, can we pay for him to join me?
There is an unwritten rule that F passengers are entitled to a guest at DXB. How that's managed for QF awards, I'm not sure. The other option would be to pay USD250 for F access.
Do you get pyjamas on day flights in first (6-7 hours?)
Not usually, but you can ask - they normally have some on board.