This is not good at all.
He is in alot more trouble than just driving unlicensed
I would strongly suggest that he hire a solicitor the practices in criminal law, as the court will not be lenient on him at all. If he has not been sentenced and has 3 similar charges in relation to driving unlicensed and now driving an unregistered and uninsured vehicle he is facing a jail term.
The court will take this as a total disregard for the rules and if they allow him to walk away, that he will simply ignore the rules and do it again.
He will need to be represented because he is facing a possible jail term.
The following is what he can receive for driving whilst suspended or disqualified
If you drive a motor vehicle in South Australia whilst you are disqualified from driving or your licence is suspended, whether that is the case in South Australia or any other Australian State or Territory, you will commit an offence that is punishable by six months imprisonment for a first offence, and imprisonment for 2 years for any subsequent offence.
in relations to the unregistered vehicle is looking fine of up to $7500
as assembly is a very serious charges and he should be represented in court and not appear on his own.
The links I have given you also provide information to exemptions but I think in your partner's case is going to have difficulty.