The connection at AKL is a breeze, your parents won't need to clear immigration or even security. The lounge is a little hard to find, though - tell them that after they arrive, they should walk along the main corridor towards gate 1, keep going straight ahead, up a slight ramp, and after another 30m or so into the corridor across from the record shop. The lounge is upstairs, on their left when they get to the top of the escalator.

NZ don't have ther own lounge in SIN, instead they use Singapore Airlines' SilverKris lounge.

Cheers, Zac