Another unusual surname and little information online about this family made me look into them a little further. The name seems to have originated in Germany, and presumably Dulcie's father and relatives came to NZ from Germany, although they may have come via Australia.
Their third child was Balfour Herbert Tetzlaff. He was born in 1900 and in 1925 he married Ivy May Johnson. Balfour and Ivy had at least three children. A son called Ronald (presumably named after Balfour's younger brother), born in 1929 and a stillborn baby in 1933. They also had a son, Douglas, born in 1931, who died aged six years old, after falling off the wharf on the Waikato River opposite Mercer on 8 February 1937.