Congrats on the upcoming big birthday, and on choosing to spend it with your adult children. I disagree with your wife (despite not knowing you or your kids) - something something skiing something something hard to clash when you’re busy having fun. It’s your first trip - why not one ski day in each, weather depending. We were intermediates when we first visited NZ and my fave of all 4 was Treble Cone, absolutely hated Coronet Peak, loved Remarkables and felt Cardrona was too much hype and crowds for not such a stellar experience. If it was a different day those views may have been different also. Definitely get a 4wd and chains and be prepared to use them (don’t wear Jandals for the drive PB ). If you’re looking for off snow activities see if the Via Ferrata is open (not sure if it is in Winter) - that was loads of fun.