It's hard to determine exactly how many cameras there were beyond mention in the inventory, since in some photo's it seems one hiker will hold another's camera while they are off having their photo taken by someone else, or to take a photo of the camera's owner.
For example in group shots Semyon and Lyuda are shown with cameras around their necks but are not attributed to any daytime photography. And we don't see Igor holding a camera at any time, even when snapped by others.
Elsewhere, though we know they both had cameras, best pals Yuri K and Tibo photographed each other using a camera swap at the same location.
Frame 4 of Yuri's
camera film, Film 1
, shows him taking a photo of Tibo
Frame 4 of Tibo's
camera film, Film 3,
shows him taking a photo of Yuri