They’re here, mother and daughter together, in a sun-drenched hotel suite full of cables and studio lights, to do the thing they officially dread: talk about themselves.

Members of the Kennedy family will talk plenty when and if the politics align, or the topic is just. In exchange for listening to Kennedys talk about the environment, poverty, Special Olympians, mental illness or the legacies of their departed uncles and fathers, you might — might — be able to coax something vaguely personal from them. Soon enough, they wise up, smile broadly with those teeth, thank you so much for coming and move along. That is how you keep people curious about you for more than half a century. That also keeps you safe.

Ethel Skakel Kennedy, 84, who was married to Robert F. Kennedy for 18 years and has been keeping his work and memory alive for another 44 and counting since his death in this very city, looks warily at the digital recorder I’ve taken out of my front inside pocket. That doesn’t seem like such a good idea, she makes clear.

Her youngest daughter, Rory, 43, who has made a name for herself filming and recording people’s words and actions, is seated next to Ethel on the sofa and offers a sympathetic, even collegial half frown, as if to say: Tough break — don’t waste your time trying to sway my mother. Look how long it took me.

Rory — who has made plenty of notable award-winning and Oscar-nominated documentaries on topics as varied as Appalachian poverty, the U.S.-Mexican border and torture at Abu Ghraib — has finally made the movie many thought she would never make. The one about her family.

The Kennedy family tree

“Ethel,” premiering on HBO on Thursday night, perhaps isn’t what fervent students of the Kennedy mystique (which is still about half the checkout lines of America) may have hoped. People who think the Kennedy cake has been overfrosted surely won’t fall for it, even though the film is undeniably moving. No one in the film tells all, certainly not Ethel.

In the first few minutes of the film, Rory leads her mother to a chair in a well-lit sitting room in Hyannisport. “Why should I have to answer all these questions?” Ethel wants to know.

“Well, we’re making a documentary about you,” Rory says.

“Such a bad idea,” Ethel says with a grimace.

Kennedys don’t cry (as eldest sibling Kathleen Kennedy Townsend, now 61, notes in the film), and they don’t divulge. Ethel hasn’t granted an interview of any length or depth in more than two decades.

On this particular August afternoon, she’ll give several short interviews to outlets besides The Washington Post — revealing little — and then she and Rory will sit on a stage for 20 minutes before a couple of hundred critics and reporters during HBO’s session at the TV industry’s summer press tour. The writers are free to ask anything they want, including whether Ethel’s grandson, Conor, might one day marry the singer Taylor Swift, to whom he has been linked in gossip columns. (“We should be so lucky,” Ethel says. “You can just leave it at that,” Rory says, baffled.)

“Ethel” is first and foremost a daughter’s ode to her mother, and for that alone, it works beautifully. It’s also a love story. “You were pregnant for 99 months of your life,” Rory, the couple’s 11th child, marvels, as she gently interrogates her mother.

“That’s the first time I’ve heard it” put that way, Ethel says.

The old Kennedy home movies, used richly here, are as hypnotically alluring and golden as ever, as if they’ve been kept in something holier than climate-controlled vaults. “Ethel” is free of historians, reporters and confidants who normally provide insights in (and sometimes clutter up) most biographical documentaries. But at several points in the film, a viewer can sense the difficulties Rory was up against. She has brought a camera inside the family circle, and not just to film one of those touch football games.

“Ethel” takes a delicate approach to much of its trickiest territory. President John F. Kennedy’s assassination in November 1963 doesn’t come until 54 minutes in, an event, as Ethel recalls, that unleashed “a tidal wave of grief.” RFK’s assassination in June 1968 comes in the film’s final act, and only then does a viewer begin to wonder whether “Ethel” is still too focused on him and not her. When Rory says, “And then we lost Daddy,” Ethel pauses, then smiles tightly.

“Let’s talk about something else.”

There is, in fact, a lot else that got the gentle touch here, if not leapfrogged altogether. There was the death of Ethel’s parents in a plane crash when she was 27; the two sons Ethel lost (David, at 28, to a drug overdose in 1984; Michael, at 39, to a skiing accident in 1997). There is Ethel’s relationship to her in-laws (living or dead; the word “Jackie” doesn’t come up once); and then there are a few other misfortunes and tragedies that swept through their lives and go unmentioned. (Rory’s 1999 wedding was postponed when her cousin John Kennedy Jr. was killed in a private plane crash with his wife and sister-in-law en route to the event.)

Faith saw her through it all (Ethel continues to attend Mass every day), and as for any insight into grief and survival, she says: “Nobody gets a free ride. . . . Have your wits about you, dig in and do what you can. Because it might not last.”

The stories of “wild” Ethel — receiver of speeding tickets; ski-slope demon; alleged horse thief; sticking her tongue out at cameras — go only so far. To compensate for her mother’s circumspection, Rory turns instead to her siblings. To a person, they describe the feeling of being introduced and honored as RFK’s descendants, heirs to his legacy of public service, and never introduced as the product of Ethel.

“It makes me so mad,” Courtney Kennedy Hill, 56, the fifth child, says early in the film. “What about the one who delivered us and carried us for nine months and has been with us for the last 40 years?”

‘It’s the hardest movie I’ve ever made,” Rory Kennedy says, looking back. “It’s not my comfort zone.”

The only reason she made it all was because Sheila Nevins, HBO’s longtime head of documentary films, who has backed and aired several of Kennedy’s projects, pestered her for years to do it. At some point, it’s almost journalistic malfeasance to ignore the fact that your best story might well be the famous family that raised you.

Kennedy considered making a film about her Uncle Ted. She thought about making a movie about Hickory Hill, the McLean acreage where she and her siblings grew up. (Ethel sold it in 2010.) These ideas were fine but skirted the real story.

“I always resisted, but Sheila was persistent,” Kennedy says. “And so finally I told her: ‘I will just ask my mother. She will say no,’ but . . . [Ethel] said yes. And I said ‘Are you sure?’ . . . It was difficult, to get my mother and other family members to live through some of the more difficult moments again. But there are a lot of joyful moments, too.”

Did she let her siblings offer suggestions while the film was being edited? “I’m too smart to do that,” Rory says. “The film locked in June. I took it to Hyannisport and showed it to my mother and some of my siblings. The first thing I did was explain what ‘locked picture’ means.”

When the movie ended, she says, “My mother was very gracious and positive about it. Which was enormously reassuring.”

“If possible,” Ethel says now, “it made me more full of admiration for Rory, how she took nothing and made it something.”

Nothing?

Rory rolls her eyes. “She’s going to deflect everything you ask her onto me,” Rory says. “But it’s nice of you to say that, Mummy.”

Here they are not Bobby and Ethel; they are Mummy and Daddy. The first third of the film is about the 1930s, ’40s and ’50s. College hijinks, family ski trips (Ethel first fell for Bobby when she met him during a 1945 winter vacation at Canada’s Mont Tremblant); sailing jaunts, mugging for the cameras at swimming pools; demerit points for mischievous Ethel Skakel and her pal Jean Kennedy at Manhattanville College of the Sacred Heart; pictures of Mummy and Daddy’s 1950 wedding (21 ushers!) and a Hawaiian honeymoon.

There is so much film of the young Kennedys and Skakels — and there would be even more had it not been for a warehouse fire decades ago that wiped out most of Joseph P. Kennedy’s private film archives. That is something to know about the rich: In addition to being frequently photographed, they got the point of home movies before the rest of America discovered Super-8mm. Joe Kennedy was one of the founders of RKO and embraced the technology; Jack’s historic campaigns and presidency assured that every scrap of existing film would be preserved. The Skakels also hired cameramen to film their family gatherings.

But not all of it was as easy to find as you’d expect, Rory says. What’s available in the catalogued Kennedy archives is one matter. The Skakel films — crucial to a documentary about Ethel’s life, rather than Bobby’s — had been transferred to video, which drifted through the Skakel family and took some effort to track down. They were finally discovered on the floor of a closet of the presidential library. A family friend volunteered to comb through Ethel’s attic of disorganized Kennedy ephemera looking for the only known photograph of a seal that lived, for a short time, among Hickory Hill’s many horses and dogs. “Climbing up to the attic and going through all that stuff — that’s a nice job to give someone, isn’t it?” Ethel says.

Viewed another way, “Ethel” is also about Rory. The film doesn’t show those pictures from that horrifying night in the kitchen at the Ambassador Hotel, as poor Ethel cradled her wounded husband and begged everyone to step back. Ethel was nearly four months pregnant then. That was Rory.

She was born in December of that year, forever assigned the role of being her mother’s bittersweet joy.

She never knew Daddy.

In a way, this central fact of Rory’s life makes her an emblematic figure of Generation X — the kids who were reminded by our older siblings (and the history books) that we were born late. It’s a refrain for this generation; we know the pictures and the songs and the moments. We have loads and loads of documentaries to watch. And yet the thing we want most is kept at a nostalgic remove. “By the time I was born, part of the story was over,” Rory says in the film’s narration.

Children are curious, she says now, in order to “understand your own narrative in a family, in any family. My daughters, for example, now want to know what I was like as a little girl.”

Filming “Ethel,” Rory says, at last gave her the opportunity to ask the questions she always wanted to ask.

She didn’t quite get all the answers, but she got a chance to get her mother to look back at her own life and try to admit, for the record, that she did a good job. That she raised decent children and instilled them with strong values.

“I think that was the other gene,” Ethel says near the film’s conclusion, meaning Bobby.

“You raised us, Mummy!” Rory objects.

“I just don’t feel I can take the credit,” Ethel says, unwilling to concede. “I just don’t feel it.”

Ethel

(100 minutes) airs Thursday Oct.18 at 9 p.m. on HBO.