Thanks, Harry. Yes, that makes sense. He must have arranged to emigrate to NZ with the Leece family but became too ill to leave with them. And yes I agree with you that John Dumbell must have sponsored his half-brother James Leece and family to go to NZ. It was quite common during the 1870s/80s for one member of a family to emigrate, and then to sponsor other members of his family to come after him.
Sue