Hamilton, New Zealand

Mark, this would be fun to figure.
I cannot tell if this is a keystone frame, front is masked, looks like V-twin of 42-45 degrees, the FRONT EXHAUST is baffling. Intake manifold(?) is high(I see front spring parts) which says IOE Indian, that intake could be a custom wire housing?
I am not into Douglas, the chassis' look LONG(no tranny), meaning pre- 1915? On the other hand at far left the chassis looks SHORT(no tranny), again pre 1915.
As a shot in the dark, I have not checked, Royal Enfield or BSA flathead 45 degree(?) twin, which were RARE for either to make, possible.

I am fairly sure that is an Indian Powerplus on the left. It must be new as it does not have the tank top tool box that the earlier ones had. You can just see where the link to the leaf spring is on the front forks.

Far left is a stumper. Whatever it is I THINK that a "sidecar" is attached. That backrest gives an impression(?) of being a spare, so I would go for an arms manufacturer that made motorcycles secondarily.

Domenic. No evidence of war as all the new Zealand soldiers were away fighting in Europe. Neither pre or post-war but perhaps during. Photo caption clearly says circa 1917.

Dominic Politi asks 'what year' for the bike photo. It is captioned 1917 and that would be very close to correct. The other photos are also date.

The bikes in the main picture appear to be mostly Douglas flat twins with an Indian (maybe a Powerplus?) at the far left.

There may have been a preferential tariff system from the beginning of car importation - https://en.wikipedia.org/wiki/Automotive_industry_in_New_Zealand - but it didn't stop American cars from being very popular here as they were more suited to the road conditions. The survival rate of American cars is also much higher with American makes being most popular in the pre WW2 section of the Vintage Car Club.

Cycle photo "exact year"(pre or post-war) would be illuminating. No evidence of War?
Attention is deferred to rider without cap, one of four on a Douglas(?) opposite opposed in line twin. This design was used by H-D, 1919-1923, but by 1923 BMW and a "plethora of German manufacturers" were founded who solved the massive problem in THESE of rear cylinder overheating, by mounting the opposite opposed engine transversely.