The characters are shown as having backstories--you get flashbacks for many of them to before they were incarcerated--but it's usually just them and a significant other: a romantic partner, mostly (husband, girlfriend, boyfriend). Sometimes they speak about having parents and the trauma of missing a parent's death (or, conversely, what jerks their parents were). But never brothers or sisters or kids.

I'd posit that creators of TV shows are answering a desire of viewers to be the center of attention and the site of all pain (so if there's a loss, it's the loss of a protector-figure, not the loss of someone you had the care of, and the suffering is all **your** suffering, whereas the women I work with seem to be keenly aware of the suffering of those on the outside--suffering they've contributed to (whether it's their parents or their kids).