From what I know the 16 year old applies in their own right therefore they need to meet the residency requirements on their own. So for example if they did not join you until March 2015 then they are not eligible until March 2019.
Out if curiosity were you in Australia on a different Visa before you got your 309? Your time line indicates that you are not eligible for citizenship (under the current rules) until the end of the year.
Out if curiosity were you in Australia on a different Visa before you got your 309? Your time line indicates that you are not eligible for citizenship (under the current rules) until the end of the year.