US Passports expire 1st week of March 2019, dont have 6 months life left to meet the entry requirement when our entering Australia first week of November.

Not the case at all. HKSAR requires ETA, also is subject to the AUD20. On top of that, you probably are not aware either, HKSAR, Malaysia and Singapore passport holders are required to submit additional information, such as HKID card number for HKSAR. Same for Malysian and Singaporean to provide their countries' ID card numbers.

So if you are not familiar / dont know the laws (your own country's laws), please do not speculate.

Besides you either have not read my earlier posts as I have mentioned how we obtained our ETAs or totally missed them. I have repeatedly mentioned that we did not apply the ETA ourselves directly. It is handled by Guy Betsy whose thread is the TOP STICKY in this very forum.
I have mentioned MULTIPLE times here how Guy has helped many FTers. We who have used his service, have posted how we Pay It Forward with the fee we saved.

I suggest you to read the STICKY so to understand Guy Betsy's project. All our 3 ETAs, 2009, 2016 and 2018 were obtained with his service. The saved fee were paid forward to our chosen charity work(s). We used commercial services for our earlier visits before learning about Guy's project.

I do encourage readers from countries that require ETAs to enter Australia, READ the STICKY, accept Guy Betsy's generosity to provide a free service then put their saved ETA application fees to much better use.

FYI, Travel Agency / Airlines can access the ETA service free of charge, regardless what passport the ETA is for. Therefore Guy Betsy can offer the service to the community so we can all Pay It Forward.
In fact, if you are BNO - British National Overseas passport holder, you can only apply ETA thru Hong Kong Travel Agents or Airlines. You cannot even apply directly. Though that does not apply to HKSAR.