Mum is Gold, I am silver, sister (u18) and father bronze. Never had any issues with accessing priority check in when travelling together with mum's Gold status. Although I'd say 30% of the time the check in counter staff neglect to put on the priority bag tags, but still most times all the bags are checked through with priority tags. Also use the business class boarding lines even when travelling in Y, although sometimes that line is moving so slowly your'e better off in the normal line.
Of note, despite being over the allowed guest limit (two over 18 guests + u18 child), QF J lounge in HKG recently had no qualms in letting us all in. Not sure if they thought I was under 18 or just didn't care, the lounge was not very busy until about 25 mins before boarding. Very glad because the main terminal is quite chaotic and the HKG lounge has great views out over the apron and is an excellent place to unwind before the overnight trek back home. Despite reduced guest capacity given the renovations 2 of us still got in as guests in MEL domestic Qantas Club,.