He married Caroline Mary Hellan Harvey about 1910. [1]
Sources
↑ "Births, Deaths & Marriages Online", [digital index], New Zealand Department of Internal Affairs (www.bdmhistoricalrecords.dia.govt.nz), Marriage Registration of Andrew McIlwaine and Caroline Mary Hellan Harvey ; citing Marriage Certificate 1910/2378 .
"New Zealand, Civil Records Indexes, 1800-1966," database, FamilySearch (https://familysearch.org/ark:/61903/1:1:QG6K-WWGL : 4 January 2018), Andrew McIlwaine, 1929; citing Death, New Zealand, registration number 1929/10369, Archives of New Zealand, Wellington.