Don't engage in silliness about purchasing and refunding air tickets. QF can simply issue you a gate pass which looks just like a boarding pass, but does not contain flight information. That and your valid photo ID will get you through the checkpoint with your parents and to the gate. If they have lounge access, you will be their guest if they have a guest.

It is not a problem and carriers much prefer it to mobility assistance when the assistance is not required and all you are providing is social company.