You Had Me at I Do

The short answer is "No".  Under Commonwealth law, a marriage cannot be solemnised unless the civil celebrant or minister has received a Notice of Intended Marriage (NOIM) signed by at least one of the parties to the intended marriage, no less than one calendar month prior to the date proposed for the marriage (and not more than 18 months in advance).  

Marriage of a person under 18 years of age requires an order of a judge or magistrate in order to be valid.  However, the law of the Commonwealth of Australia also provides that under no circumstance can two persons who are both under the age of 18 years marry each other.  

It is always adviseable to check with the local municipal council and/or management body (Eg: NSW Parks and Wildlife) to find out whether permission needs to be sought to hold wedding ceremonies at outdoor venues such as parks or reserves.  Some councils will require a fee to be paid to cover costs of liability insurance in the unlikely event of an accident.  There are certain parks and reserves that are able to be used free of charge.  There are some parks and reserves in multiple locations that are "free of charge" for weddings and elopements.  Google "free elopment locations in [the area you wish to get married in]".

Your Official Certificate of Marriage and Commemorative Marraige Certificate which is signed after the ceremony, must be signed by the Bride and Groom and each of their signatures witnessed by a person of their choice, provided they are over the age of 18.  The celebrant must also sign these documents.

The Notice of Intended Marriage (NOIM) which is completed, signed and submitted to the celebrant no less than one calendar month da prior to the ceremony can be witnessed by an Authorised Marriage Celebrant or other authorised person as specified on NOIM.

Your Declaration of No Legal Impediment which is to be signed just prior to the ceremony, is to be signed by the bride, groom and your celebrant.

I have a Mipro Wireless PA system which is battery powered and bluetooth capability.  Whilst I can play music through my PA system, for the sake of a seamless transition between operating music for arrival, signing etc and the celebrant orating, I strongly suggest that the bride and groom allocate the job of music for the ceremony to a trusted guest and provide their own bluetooth speaker.   I can provide a bluetooth Sonos speaker for this purpose if required but it is preferable to use a bluetooth speaker that is already paired to the device providing the music.