Visa application for a New Zealander wife and son while in Singapore

Hi, I am Singaporean and I live in Singapore at the moment but my wife and son hold a New Zealander passport. They plan to apply for a 6-month double entry visa for China when they are in Singapore visiting/ staying with my parents. Visiting China will depend on my parents' health hence why wife and son will not apply for the China visa while in New Zealand but rather do it in Singapore when our plans to visit China will be more firm/accurate. Please advice