Hi

Flying soon Heathrow -> Hong Kong -> Sydney -> Brisbane in one 28 hour hit.
2.5 hours in Hong Kong, but only 1hr 50 in Sydney between landing and onward flight to Brisbane 9including a terminal change.
All booked via BA website in one go.
After bag check in when will we likely next see our bags (fnaar fnarr, no jokes)?
I'm assuming HK transit will be straightforward - but where will we go through customs/immigration in Oz, and do we have enough time in Sydney to pick up bags (if needed) and transfer for Brisbane flight?
What happens if we miss Brisbane flight?
Any words of advice/wisdom?

LHR HK is BA, HK Sydney is Cathay, Sydney Brisbane is Quantas.

Many thanks!