I didn’t address the point because a lot of my family’s old photos look like this. Twins become more common later. But also i expect the actual age gaps represented in this photo might not be so close. The children on the right are likely not children at all.
Also genetics has to play some part here. Women in my family have relatively few complications in childbirth, and recover more quickly than usual along with their libido apparently, so just a few months between birth and pregnancy is common.
I’m just trying to offer a plausible alternative explanation that I can vouch for so you don’t have to imagine this nightmare.

I fully agree with you re: most of your points, and don’t necessarily disagree otherwise, just trying to not expect the worst of people I don’t know based on a photo <3