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Few subjects generate as much contention and heartache hereabouts as siblings and the role they play, or don’t play, in caring for aging parents.

The last time we talked about this, lots of beleaguered commenters blasted their brothers and sisters as “heartless,” “useless” and “breathtakingly self-centered” for having opted out of the burdens of elder care. “I will never know them again,” wrote Julie from Mendocino, Calif. “No great loss.”

Which led me to wonder: What about those absent children? What’s the view from their side of the divide?

Cynthia Barnes has learned to keep her distance, she told me, and hasn’t seen her mother since the summer of 2009. Still healthy and active in her early 80s, her mother lives with her son and his family in a small Midwestern town, where she helped them buy a house with a mother-in-law apartment.

Her mother has declined to visit Ms. Barnes in Colorado, even if she buys the airline ticket. And after an ugly blow-up on a family vacation, Ms. Barnes hasn’t made the trip to see her mother. Mother and daughter restrict themselves to brief phone calls.

In Ms. Barnes’s view, a long history of painful interactions necessitated her withdrawal from direct contact with her mother: “It’s always been a very difficult relationship.”

Ms. Barnes said she twice had agreed to bring her mother into her home. The first time, she and her then-husband owned a duplex in Michigan and gave her mother the first-floor apartment.

“She criticized everything I did — my housekeeping, my weight, my not being sufficiently deferential to my husband, my letting cats on the furniture,” Ms. Barnes recalled. Ultimately, when Ms. Barnes and her husband divorced, she said, her mother called her some very unpleasant names. They didn’t speak for months.

A few years later, Ms. Barnes had remarried and bought a triplex in another state. She again agreed to her mother’s request to move in. “Amnesia,” Ms. Barnes said. “Hope springing eternal.”

This time, “I removed myself when she criticized me,” Ms. Barnes recalled. “I established the ground rule that once she hurt my feelings I was leaving, going upstairs to my own apartment. And in less than a month, she left.”

Ms. Barnes still visited her mother, though, until a traditional family beach vacation in Florida. As Ms. Barnes recalled the incident, her mother — who abstains from alcohol and berates family members who don’t — grew enraged when people began mixing evening daiquiris.

“She got really abusive,” Ms. Barnes said, even going so far as to threaten to throw scalding coffee at her daughter. They haven’t seen each other since.

“I’m sad, and I wish it were different,” Ms. Barnes told me. She loves her mother; she believes her mother loves her. She feels bad that her brother will shoulder the day-to-day burden when her mother falters. Ms. Barnes is willing to participate, even from a distance, but said her brother hasn’t responded to her repeated offers.

So an uneasy detachment prevails. “She’s not going to change, and all I can do is try to protect myself,” Ms. Barnes said of her mother.

When I asked my favorite geriatric social worker, Barbara Moscowitz at Massachusetts General Hospital, about this sad situation, it was old news to her.

Under the best of circumstances, she pointed out, ordinary families find elder care extremely stressful. “If we learn that family life was strained — by addiction, physical or emotional abuse, poor parenting — and that children, to save themselves and find their own lives, had to move away, we can’t suddenly assume that a family with that history can just step up and give care,” she said.

Of course, our nonsystem of elder care, which relies so heavily on families, does indeed assume that sons and daughters (primarily the latter) will step up. But without a familial history of respect and warmth, Ms. Moscowitz pointed out, the stresses of caregiving can actually become dangerous. It’s family members, not outsiders, who are most likely to abuse or neglect old people.

In her practice, for instance, Ms. Moscowitz worked with a son caring for a mother who had always been judgmental, demanding and unpleasant — and whose dementia was intensifying the problem. “The son’s anger and stress was escalating to a point where he needed to be out of the line of attack,” Ms. Moscowitz said. She became especially worried when he called, guilty and ashamed, to report that he was beginning to shout back at his mother.

Her progressive disease meant that family counseling was unlikely to accomplish much. The son’s best chance at preserving a relationship, Ms. Moscowitz advised, was to transfer responsibility for his mother’s care to the staff at a quality assisted living facility, and then to visit regularly.

“Not everyone was made to be a caregiver,” Ms. Moscowitz said. “For some children, it’s just not emotionally possible.”

“But that doesn’t mean they’re off the hook,” she added. “They have to work with their siblings — and others — to figure out what kind of contribution they can make to help the family.”

Handling the bills or Medicare paperwork, stepping in to allow primary caregivers to take vacations, sending monthly checks — these adult children can support their siblings, even if they want little to do with their parents.

In a perfect world, we’d all have access to a comprehensive geriatrics practice like Mass General’s, with social workers like Ms. Moscowitz, to help work out such arrangements when emotions run high.

Failing that, people can hire geriatric care managers, who are also usually social workers, or bring in family mediators. Or turn to lower-cost social service agencies that often provide counseling on a sliding scale. Or consult Francine Russo’s book, “They’re Your Parents, Too.”

Because eventually, ailing parents will die — but siblings and their families will remain.

Ever the social worker, Ms. Moscowitz frets about people she’s never met — like Cynthia Barnes and her brother. For the sake of their later relationship, for Ms. Barnes’s own future mental health, “it might be important for her to feel she’s done her best,” Ms. Moscowitz said. “To do what she can do.”