Never had any major problems myself when flying on QF. Latest was when my Mum, Dad and Sister were travelling together on QF. All three got into the First lounge with no issues.
When travelling domestically (4 of us), there never has been a problem getting into the J/C lounge (even since both myself and my sis have not been under 18 for a couple of years now). This has usually been off-peak though, and I guess a WP is allowed 2 guests anyway.
For entry into the F/C lounge, the rules have only been relaxed when flying QF (and not say on CX - which I think is fair enough). When flying CX once (4 of us) to PEK, we were directed to the J lounge, despite being nice and joking it was because QF do not fly to PEK
- This was after the guy at the entrance even commented (in a joking way) "if you were flying with us we could let you all in". J lounge accepted us conditionally as a one off (we were flying in Y).