Ji-li's eleven-year-old brother (Ji-yong) and ten-year-old sister (Ji-yun) are in the background for most of the book. Much of the time, we get the sense that Ji-yong would rather play outside with his friends than anything else, but that doesn't mean he and his sister aren't a source of major worry for Ji-li:
The worry of tomorrow haunted me constantly. […] I worried that Ji-yong's temper would get him in trouble, and that Ji-yun would be so frightened that she would never laugh again. (17.7)
Ji-li loves her brother and sister and just wants the best for them. No matter what she does, Ji-li can't shake the looming fear she feels for these two.
Ji-yong and Ji-yun might only be a year or two younger than their sister, but they are certainly less mature. They don't seem to understand what's happening quite as much as Ji-li does, and they definitely don't feel the duty to take care of the family the way Ji-li does. It must be nice being the younger siblings.