I feel you on the NZ PPT-AKL flight timing... it's awful especially with young children. Note that even if you book under the NZ flight number on the TN flight that Koru benefits, including lounge access, don't apply in PPT. Gold and Elites get one guest for lounge access but that may or may not include kids depending on how TN applies its own lounge rules. The PPT lounge is part of Priority Pass though, which is an option.

If I were you I would just book TN. You need to collect your bags in AKL anyway, and if you book a FlexiTime (or whatever it is called now) for the domestic leg you have some protection against a delay on the inbound TN flight.

Note also that NZ often sells its block of seats on the TN operated flight at a premium to what TN will sell it - ie you should come out ahead and pay less if you book a TN operated flight through TN directly rather than through NZ.