Can you give the rest of the information on the birth certificate for Albert please.
Previous issue would be mother's history. Charles might be a child born to Martha before she met Charles snr.
The names on passenger list might not be them...Charles Davis is very ordinary name.
Birth Certificate from Orange NSW for Albert John DAVIS.
Fathers Name: Charles Davis
Occupation: Butcher
Age: 31
Born: Exeter Devonshire England
Present or not: Not present
Date of marriage: 28th November 1881
Place: Exeter England
Previous issue: 1, Male, living
Mothers Name: Martha Steven
Age: 22 yrs
Birthplace: Torquay England
Witness Dr Heinermann & Mrs Smith 16th November 1886 Orange