Everyone wants what is best for Mom. But when an aging parent receives a dire diagnosis, old scores, rivalries and pecking orders from childhood can come back to haunt.

Siblings may spar over the merits of assisted living vs. in-home care. The oldest may make a critical decision without consulting the others. Another is focused on who will pick up the tab.

“Nothing reveals the fault lines in sibling relationships like the seismic shift caused by an aging parent’s sudden decline,” Philadelphia psychologist and consultant Barry Jacobs writes in Psychotherapy Networker.

The more siblings, the more conflicts. For some adult children, this is their last chance to win a parent’s approval.

“Emotions are intensified. It’s a stew of things,” says an administrator at a Northeast university who wrangled with two sisters about their late father’s Alzheimer’s care with support from a third sister. “It’s painful for everyone when your father can’t walk or talk and is incontinent. Nobody is really in their best place.” She asked not to be identified to avoid reopening old family disagreements.

One sibling typically shoulders the greatest burden. It may be the one who lives closest to the parent or has fewer family or work obligations than the others. Most often, the chief caregiver ends up being the oldest or youngest daughter or the parent’s favorite, says Jacobs, who writes AARP’s caregiving column and wrote “The Emotional Survival Guide for Caregivers.”

Today, close to 1 in 5 Americans are caring for an aging adult, according to a 2020 report produced by AARP and the National Alliance for Caregiving (NAC). That comes to 41.8 million caring for someone 50­ and older — 20 percent more than in 2015. And within that group, 1 in 4 are caring for two people.

The most common grievance of primary caregivers: “Why is no one helping me?”

On average, the person in this role devotes 24 hours per week to caregiving over a period of four to five years, according to the AARP-NAC report. This, while the majority hold other jobs, too.

“It’s not just the very little time [my brother] spends at the house with our mother, but his lack of empathy for me,” says a Los Angeles sales associate who is overseeing care of her mother, 93, with heart failure. “I’m worn out emotionally.”

Her mother and younger brother haven’t gotten along for years, she says, but why can’t he clean out their mother’s garage or help shred papers without any contact? Her relationship with her brother will not rebound from this, she says, asking to remain anonymous out of respect for her mother.

Siblings estranged from parents seldom want to reconcile, research indicates. Rather than argue with her brother, the Los Angeles caregiver relies on an in-home care agency for assistance. She knows she is fortunate the family can afford that option.

Barring estrangement, how­ever, experts urge overwhelmed caregivers not to suffer silently.

A sibling may not want to face the reality of a parent’s decline or live too far away but there are other ways they can help.

Assess who can do what in your family, says C. Grace Whiting, president and chief executive of NAC in Washington, D.C. “Not everybody is good as a caregiver, but they can pitch in for the cost of an aide.” Or a sibling who is not comfortable with hands-on care can handle finance and insurance paperwork, she suggests.

Think about what you need and approach each sibling individually, Jacobs says. “Say ‘This is important to me and our relationship.’ ” Explain you are struggling, he says, and that the sibling’s lack of support will affect your relationship permanently.

Don’t make others feel guilty or defensive but spell out how they can help. Do you need a fill-in while you take a vacation? Someone to research and order an assistive device? A persuasive voice to get Mom to give up the car keys?

“People are afraid to raise the stakes too high but the alternative is that you feel extremely resentful and it will not be a good relationship anyway,” Jacobs says.

Sometimes, long-distance siblings aren’t helping because they don’t realize the level of care a parent needs until they visit for the holidays, Whiting says. “I’ve been telling you,” the caregiver replies, exasperated.

This is especially true of dementia, says social worker Christina Irving, client services director at the Family Caregiver Alliance in San Francisco.

“You may have one sibling overreacting and another underreacting,” Irving says. “The person more intimately involved with the parent sees the nuances. The things you only see when you spend the whole day with them.”

Other tensions erupt when the person in the caregiving trenches is criticized by out-of-town siblings. The university administrator who was the primary caregiver for her father felt judged by two of her sisters.

“You’re lifting a huge burden off your siblings,” she says. “I don’t want to be giving my father a shower — are they aware of what that’s like?” Besides a demanding job, she had a husband and two children at home then.

Her family was also divided about whether to invest in an expensive but unproven drug that was thought to slow the progression of Alzheimer’s. Her father had enough savings to cover the cost but two of her sisters questioned the value and expense. Ultimately, she chose to buy the medication.

“It’s an ugly thing that lurks: how much money will be left at the end,” she says, and it came up again. All the sisters had agreed on renting a condo for their father nearby her home and hiring an aide. But when the condo owner decided to sell it after several years, she and one sister wanted to buy the unit so their bedridden father, 94, could stay put. Her two other sisters wanted to find another rental to minimize costs.

She considered buying the condo anyway with her father’s savings. “I just wanted [my father] to have a peaceful death.” But ultimately, she put family harmony first.

“It was a huge undertaking,” she says about finding a new rental and moving her father. “But he’s been gone almost 10 years and I’m happy I maintained relationships with all my siblings.”

Caregiving doesn’t have to drive a wedge in families. “When someone gets sick or disabled, it tests your values and how you communicate and handle a crisis together,” Whiting says.

Mark, a journalist in Colorado, says he feels closer to his brother and sister since they began caring for their mother. “We talk a lot more often than we used to,” he says. “We have similar frustrations and worries.”

While his younger brother in Philadelphia is on the front line of his mother’s daily care, Mark and his sister in Canada keep in close contact over email and in conference calls. They help with Internet research, daily check-in calls and provide respite care.

One factor behind the successful collaboration is that the three met together with Jacobs over Skype for guidance. They talked through challenges such as concerns for their mother’s safety and her resistance to getting an aide.

Other families have turned to elder-care mediators or geriatric social workers to help them get beyond impasses.

“Find a professional who can draw you a map,” Mark advises other caregivers.

The biggest mistake caregivers make is not starting conversations earlier with parents about advance planning, Irving says.

Ask parents what quality of life looks like for them and where they want to live in their later years, she says. Being able to respect a parent’s wishes can circumvent sibling infighting later.

Despite the challenges, the university administrator says that caring for her father during his last 10 years taught her about the arc of life and how to keep things in perspective: “It’s one of the most important things I’ve ever done.”