I think that the advice about needing a visa for your partner is very sensible and required: My general understanding is that an airline can't check you in on the SYD-HKG leg, even with a separate different booking, unless they can see a visa for HKG as that is for that explicit booking. So I believe you need to plan this in. I'm speaking about this conceptually, as I've no idea if Cathay (or Hong Kong) will be more flexible.

Note: In hindsight booking 11 months in advance, it likely would have been easier to wait and book it all together, avoiding this visa trouble and missing your flights (Doesn't apply if you are flying at CNY when early booking makes sense). If you need to go airside or pick-up and drop bags then 2 hours at HKG isn't enough, see this thread: Manual transfer HKG - 2:45