Perhaps that's partially the point? They've all been brought together in a manner that, for almost everyone, is uncomfortable and strange... to say nothing about the nature of the connection they share which is awkward, even to them.

Meh, I think they all look like they’re trying hard to look like they’re not enjoying it, aka hipster, it’s not cool to be happy

FWIW, as someone who found out by surprise that I was a sperm-donor child (and that I have at least one half-sister who was equally surprised by the knowledge of an unexpected half-brother) I find the expressions of the people in the photographs extremely relatable. It's pretty much the exact expression I had on my face when I first found out, which is essentially a combination of "wow this explains a lot of things" + "what the fuck" + a constant background oscillation of "but this changes nothing/everything/nothing/everything/nothing/everything". I'm in my mid-40's, so it's not a generational thing.

I do think there's the factor of the type of camera used: it's mentioned that it takes a while to take the picture.