You and your family are certainly experiencing all NZ has to offer. I haven't been to Greymouth, but Bernie Pullen just took the TranzAlpine train from Christchurch to see all of the amazing landscapes. You'll enjoy your ski trip to Queenstown. I caught the Skyway up the mountain.My daughters went snowboarding. The views from the top are worth it. Here's the story of Niall's hike.

https://medium.com/globetrotters/i-miss-having-a-mountain-in-my-backyard-288d589ba8e4