“The importance of relationships with brothers and sisters is terribly underrated,” says Ingrid Arnet Connidis, PhD, professor of sociology at the University of Western Ontario in London, Canada. “Adult siblings have seen the inside of you more than most people ever will. They’ve seen you at a stage and in a milieu where you expose yourself differently than you would in other environments. You don’t get to choose how to portray yourself with siblings; they already know who you are. It’s a basis for vulnerability but also for feeling very close later in life, when you’re looking back. They’ve known you and known what’s mattered to you.”

Sibling relationships start off as involuntary but in adulthood become optional. We can take them or leave them, and often we do leave, at least for a while, heading off to attend college or pursue a job or simply explore what kind of adult we wish to become. The family’s close knowledge of us usually ends when we exit the home, but their image of us continues, often becoming fossilized. “I have an 86-year-old aunt, and because she was the youngest, everybody still considers her the baby,” says psychologist Caffaro. That inability to change position can be quite literal: Mediator Blair Trippe of Norwood, Massachusetts, says that when she works with families to resolve eldercare disputes, siblings typically choose the same seats around the conference table that they occupied at their childhood dining table.

Such a fixed familial stance spells trouble in the caregiving situation, because everything you hear and say may be filtered through the lens of how things once were. “If you were a kid who felt left out a lot, you tend to experience whatever happens with your siblings now as if that were still going on,” says clinical psychologist and mediator Jane Ginsberg, PsyD, who is based in Cape Cod and Denver. “If you were the oldest kid and felt as if you had too much responsibility when you were growing up, you may walk into the family situation and feel you have to take it over—whether you want to or not.”

At one point during my father’s last years, my sisters and I spoke or met or e-mailed on a daily basis, comparing notes on a new drug’s efficacy or deliberating whether our father’s $300 loan to his home health aide (so that her husband could buy carpentry tools) was OK or suspect or any of our business. One day, at a meeting in Margaret’s kitchen, I became furious with Diane, who was reporting on a conversation she’d had with a doctor. Every question we asked seemed to prompt a rebuke from her, as if we weren’t listening hard enough or didn’t have a right to clarification. Bossy oldest sister! I fumed to myself. What gives her the right to be so angry? Margaret, on the other hand, pulled a classic birth-order move and began a middle-sister mediation, speaking to Diane with tender sympathy. “It’s hard to keep all this information straight, isn’t it?” she asked.

Diane broke down in tears, the tension evaporated, and we all had a chance to refocus the discussion on Dad’s needs, not our own conflicts. I’m pretty sure that meeting ended with a power-of-three group hug.

Afterward, I couldn’t stop thinking about what had happened. What stuck with me was just how transforming compassion could be and how unable I had been to enlist it. I’d always valued that I could be myself with my sisters, but here I saw that it wasn’t always my best self that showed up. In truth, like many of us, I probably put more effort into making nice with the UPS guy than with my siblings.