There is no legal barrier to adults choosing to have the same surname, regardless of whether they are in any type of relationship. Doing so has no legal effect on the status of the relationship but it may remove a lot of practical difficulties, particularly for de facto couples (in such matters as hospital benefits, making contracts, obtaining a loan), simply because there is likely to be less explaining to do.
You can change your surname by applying to Births, Deaths and Marriages Victoria (see ‘Contacts‘). Information and forms may also be obtained and lodged via the Births, Deaths and Marriages website. (For further information, see Chapter 4.6: Changing your name.)
The surname of children of a de facto relationship is also discussed in Chapter 4.6: Changing your name. Note, however, that one parent cannot change the legal first name or surname of a child without the other parent’s consent or a court order. See ‘Registering children conceived with reproductive assistance and through surrogacy arrangements’, below, for information on registration of children born to same-sex parents.
In Zalsman and Blendall  FamCA 292, the applicant mother filed an initiating application seeking a change of surname for her four children. The mother wanted her children to adopt her surname and not have the surname of their biological father, Mr Blendall. At the time of the hearing, the mother had sole parental responsibility of the children. Also, an intervention order was in force against the father due to significant domestic violence perpetrated by Mr Blendall. Evidence was given by all four children that they wished to change their surname so they would no longer have a surname that they associated with an abusive past. As the court found that a change of surname was in the best interests of the children, it granted the orders sought.
In contrast, in the case of Howells and Parry  FamCA 414, an application by the father to change the surname of the child (Z) was dismissed as the court was not satisfied that the change of name was necessary or in the child’s best interests. Also, there was no significant confusion that would be allayed by changing the name of the child, and no pressing need that would outweigh the practical difficulties caused by the change.