my parent did it in aus. just case by case. they had to do chest xray and pay for that new visa to extend.better to do early before the current one going to expire. it takes time.
Did you parents try to apply a longer visa when they applied the visa when in hk? Or they extend the visa in Australia? Do you know how much is the fees?
applied 3 month visa in hk. another visa was applied in aus to stay longer.as i remember the fee is almost the same as you apply in hk.
if you haven't applied any yet, do 1 year in hk. need not submit 2 applications separately.