I think the answer to your question may be that you will need to ask Queensland's Registrar-General in order to find out.
The process is described on a Queensland Government page entitled Applying for a birth certificate which says that your husband will need to:
- Include proof of eligibility
To determine that eligibility there is a PDF on the same site entitled Certificate Access Policy which says:
3.1 Section 44(2) of the Act states that unless the application relates to historical information, the Registrar may refuse the
application if the applicant does not have an adequate reason for
obtaining the requested information or certificate.
The Act also
requires that in determining an applicant's eligibility to obtain the
requested information or certificate, in respect of a registered
person, the Registrar must have regard to
- the relationship, if any, between the applicant and the person to whom the information relates; and
- the reason that the applicant wants the information; and
- the use to be made of the information; and
- the age of the entry; and
- the contents of the entry or source document; and
- the sensitivity of the information; and
- any other relevant factors.
In satisfying the above factors, the prime concern is that adequate
care needs to be taken to prevent unjustified intrusion to privacy of
an individual and to prevent information being obtained fraudulently
or improperly, but not hinder those persons who have a legitimate
entitlement to the requested information or certificate.
I have no legal background but I think this may say that such applications are treated on a case by case basis. I would expect that your husband being her child would have more chance of obtaining it than anyone else.