The A4 and Passat are the same car underneath (Both Volkswawgen group). If you like the A4 but maybe want something a bit lower cost, the Seat Exeo is the 05-07 Audi A4 with some altered panels...Dashboard is identical to the A4 convertable.
Another option from the Vw group is skoda, If you can get over the badge snobbery! Something ugly but good for the kids - skoda roomster, Low cut rear windows so the kids have a better view etc. If you want toys and legroom try a skoda superb estate, 633 litres of bootspace, Satnav, DVD, heated leather (not that you need that round your way!), self parking systems, 170bhp and around 5L/100km (2.0 diesel).........sadly ive just looked up how much they are used in NZ! So forget all ive said
Out of the choices you have given the A4 is probably your best buy, unless you can import a skoda from the uk