They were also ordered to pay reparations of $110,535.
FENZ says the incident occurred on a rural property.
Bev Hiscox and her two grandchildren, Luka and JJ Sirett, aged 10 and 5, died on Sunday.
Locals in Raetihi say the community will be there to help the family get through the deaths of a much-loved grandmother and her two grandsons.
Bev Hiscox and her two grandchildren Luka and JJ Sirett died on Sunday.
Bev Hiscox and her two grandchildren, Luka and JJ Sirett, died in the incident.
Three people died in the incident.