Partner's elligitimate child required documentations

Melgar

Just want to ask if anyone knows what are the needed documentations if my my wife had a child before our marriage and we want to include the child in our application. His paternal father is not registered in child's birth certificate, only my wife's name apprears.
Seeking legal adoption or child custody will take time, and we have not started on it as well.
Is it enough to provide the child's b-cert? and "Form 1229 Consent form to grant an Australian visa to a child under the age of 18 years" which is signed by my wife only? (we dont want to coordinate with paternal father anymore as well.
Or maybe anyone here experienced similar case. Appreciate all your input.