Hi Wendy,
The photo with 3 sons, shows two names, Bert (Albert b 1884) OR Herbert (b 1881) and Percy (b 1890). I would think that their father, Thomas Conrad SECKOLD was the other man in the photo.
The single soldier, in two photos appears to be the same man. Percy SECKOLD enlisted 1915 in Wagga Wagga, and one of the photos was taken at a Wagga Studio, so, it may well be Percy in those two photos.
Victor was living in Sydney when he enlisted in 1917.
No idea, who the older man with the moustache is. He looks like the man in the photo with the two younger boys (possibly Thomas Conrad SECKOLD).
Mary