Who are these people and why were they in Dad's papers?

When I was cleaning out my mother's house last spring, this tiny picture was down in what used to be my dad's workshop in the middle of a pile of papers that had not been touched since he divorced my mother in 1978 (he died in 1984). It was somewhere between old newspaper clipings, his childhood scrapbook and two Mets programs from 1962 and 1964. There was no clue as to who these people might be or what the interesting native costumes on the cut-off people (women, I presume) might be. After scaning it, I noticed that the house in the background looks to have a thatched roof, and that there is only a reflection of trees in the window, so the house is not on a street in a suburb or city. Other than that, I am stumped. The people - the young men in the back row look like they might be my grandfather and his brother Gene - don't appear in any other photos I have. The black-haired woman is dressed in fashions circa 1925-1928, with her short dress and muley shoes and cloche hat. But she's not in any other picture I have either. Are they family, ancestors, or just strangers or friends of someone?

Wish I knew the story, Dad.