To bring a case you have to have Standing before the court. In general terms that means you would be identified as being affected by the action contested.
Beyond those with a direct stake in SSM, there is the systemic question of the process itself and whether the funding should have gone through a Parliamentary budget process.
There are three sets of claimants;
Andrew Wilkie; the Parents Families and Friends of Lesbians and Gays ; and the broader group Australian Marriage Equality that Janet Rice is associated with. Hetrosexuals are not excluded from membership of either group.