The NZ government will insist that the GB apologise. The American GB refuses to apologize. Stalemate.
But seriously, slimboyfat is right with: "It looks like a case of: we claim all the authority, but accept none of the responsibility". They'll never relinquish their self-perceived moral authority, and an apology would do just that.
Threatening their status as a religion and also their charitable status might work, but, their pride is too great. NZ is a small outlier of their empire. They might just take the L and let go of the small number of assets they still have there. They've moved that operation to Sydney*, anyway.
*Denham Court, actually, according to the company registration data on the ASIC database.