Intrafamily adoption is a minefield that can blow up down the road and destroy family relationships. You need to consider the worst case scenario and mitigate that from happening by being very thorough in your language. There must be clarity and honesty in the parties' objectives, and as a lawyer, I would go the extra mile to make sure the transaction is considered critique-proof. I would look at the laws, moreover, draft a document that outlines the parties' intent and objectives in detail.
Of course, I will need to know the parameters under Australian law, but my input is to prevent any misunderstanding among the parties.