I really do not like responding to posts with so few & vague facts. The chances of a wrong or incomplete response are very high.
You must decide if you are actually making a commercial loan based on the facts and legal advice.
You must decide whether it is a deferred interest loan or else a capitalised (compounded) loan based on the contract.
The contract terms may contradict whether it is fully commercial, or which type and will need to be drafted carefully because you are having trouble distinguishing the difference.
If it is a commercial deferred interest loan, you will be declaring interest income each year, your nephew will be claiming interest expense each year if used for earning his assessable income. This is regardless of the fact that no interest is paid until the end.
If it is a deferred interest loan, your nephew would not be capitalising interest because no new borrowing has been made to notionally pay you the original interest expense incurred.
If it is a regular loan (or coumpounded) then there is hundreds of threads to read on this site.
If interest is to be capitalised by your nephew, then Part IVA needs to be discussed with his accountant.I wouldn't mind betting 90% of accountants will not understand and will just pick up the phone to ask the ATO what to do and then charge you for their time.
However, that is still better than the ones who don't understand and also don't ask the ATO. But they will still appear cheaper and possibly knowledgeable to you. You won't find out which until an audit occurs.
Please pay for some competent legal and tax advice before acting. Don't for goodness sake rely on a loan broker or bank employee.
Cheers,
Rob