Notwithstanding QF somehow rebranding the T3 BA lounge before June, I have a question related to the OP that perhaps goes a bit deeper.
First, the characters:
Myself, P1 (OWE)
Mum, CX Silver (OWR)
Sister, QP (no OW status)
Next, the flights:
Myself, QF2
Mum, CX254
Sister, AA107
I chose my sisters flights on AA metal specifically because from my reading, she wouldn't get lounge access anymore on BA metal as a QP member. So, from my reading (am I wrong :shock

she can use the AA lounge. My mum, as a CX Silver flying on CX can use the CX lounge. I can use a few lounges I believe, but am curious on the best route to take, as we're all leaving on the same day, my sister first at 5, before myself at 9:30 and mum at 10:30. Again, from my reading my guest only needs to be travelling on OneWorld, not on the same flight, so could I guest my mother to the AA lounge so we're all together, before my sister departs, and then head to another, better lounge? Should I be guesting my sister out of the AA lounge to the CX one instead?
It's all very confusing right now, but I figure we all have lounge access in our own rights, just separated.