Will this work?

Or possibly, could we do?

NZ --> HK --> Guangdong --> Macau --> NZ

Cheers

The main detail that has to be understood is that 144 hours visa free transit in Guangdong province, where Guangzhou is located, can be obtained only if you fly into it. So, your route:

Hong Kong - Guangzhou - Macau

Could be perfectly fine, but you have to fly from Hong Kong to Guangzhou and then exit to Macau. In order to exit to Macau, the best option is to take a ferry (catamaran) from Shekou port in Shenzhen. I am intentionally pointing at this ferry (catamaran) because you can buy a ticket for it before your arrival in Guangzhou and have a printed confirmation to present it to Guangzhou immigration authorities. Just take a look at TurboJet.

This 144 hours visa free transit allows you to move and stay within the entire Guangdong province.