You may not get the visas, so can you afford to waste the price of the tickets?
Evidence that he will go back - anything he can think of, or arrange, to show that he is due home at a certain time, e.g. meetings, acceptance of invitations to important occasions; proof of where he lives and that arrangement is set to continue; proof of future plans in home country, e.g. enrolment on a course, etc., etc.. Do a search on the forum - other people have discussed this, too. And see this page from INZ.
https://www.immigration.govt.nz/new-...enuine-visitor