It is fairly certain that all these photos were taken at Walden. The clues are in the appearance of the landscape (e.g. the buloke ‘forest’ and yards just near the family home), the distinctive front fence and gate, the distinctive verandah posts and brickwork of the house, the large fern house structure and so on.
The blotches are in the emulsion of the negative, not on his actual face and coat.
Those appear to be the line markings of a tennis court, and I’m pretty sure I can make out the two net posts. The gentleman at the back appears to be carrying a tennis racquet, but I think he is the only one. There is obviously no tennis match happening here. I’m guessing this photo was taken in 1917-1918, and its purpose is to show where Walden’s tennis court(s) were going to be built in the near future.