The factsheet section about Funds has this.
(my bolding) And here is the full regulation.
https://www.immigration.govt.nz/opsmanual/#43653.htm
I believe that your brother can write you a letter stating that he will be providing a home for you, so you will not have rent to pay. This used to be acceptable, though it is not specifically mentioned. Or possibly, INZ may require him to complete a Financial Undertaking as mentioned there. You could phone INZ to ask, if nobody on the forum has an answer shortly.