Hi Lizzie,
I understand this info may not be exactly what you are looking for but I think it may be useful anyway as there are a number of name differences amongst your aunts and uncles. This info comes from the NZ BMD registers.
https://bdmhistoricalrecords.dia.govt.nz
Walter was born on 18/4/1908;
Ida Lynne b. 1904;
Sybil Maud b. 1898;
Vyvienne Clara b. 1902;
Colin Tasman b. 1900;
Wilfred Arthur Noble b. 1912;
Beatrice Jean b. 1913;
Katie Isabel b. 1907;
Roderic Charles b. 1905;
Winifred Leila b. 1915;
Rita Aylwynne b. 1910.
If you need help with specific birth dates let me know and I can help.
Also, your grandparents, Tas and Emil G. were married 21/4/1897, Registration No. 1897/481.
When you find the above records on the NZ BDM site (above) you can order the actual certificate which may give you additional info, at a cost, if you wish.
Regards,
Kevin