I have a photo of (John) Douglas Blacklock taken in 1915 that I would like to pass onto the family. He is Charles Blacklocks brother so Mildred's uncle and your great grandfather's nephew. Photos of William Blacklock are in NZ library with photos of the family children when young at their house Matamoana. You can find the photo online at the Alexander Turnbull library in NZ. Here is the information attached to the photo.
Andrew, Thomas, 1855-1939 :[The American Vice-consul General's house, "Matamoana" (Sea-View), Samoa].Ca 1895.
Reference number: PA1-o-546-19.
Good luck and tell me if you would like Douglas's photo. I can email it to you directly.