When Sylvester Stallone's three daughters argue, the fights can become so heated, they quickly devolve into hand-to-hand combat.

"Rock, paper, scissors," explains Scarlet, 14.

"You just whip out your hand and battle," adds Sophia, 20.

Take this morning, when Scarlet and Sistine, 18, walked out of their bedrooms dressed for the day—exactly alike. "We looked at each other and were like, 'No,' " says Scarlet, who bested Sistine in a quick match, forcing her sis back to her closet.

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Victor Demarchelier
From left: On Sistine: Guess shirt, shorts, and earrings; On Sophia: J. Crew swimsuit; Guess skirt and earrings; Le Vian and Pandora Jewelry rings; On Scarlet: Guess jacket, jeans, and earrings; J. Crew bikini top; Le Vian and Pandora Jewelry rings.

When it comes to the good fight, they certainly learned from the best: Their dad wrote and starred in 1976's epic boxing film, Rocky, and won a Best Supporting Actor Golden Globe last year for the sixth sequel, Creed. He's been married to their mom, the model and beauty entrepreneur Jennifer Flavin Stallone, for 20 years. And this year will be a telling one for the family, as Sly leads his daughters into the Hollywood ring to show their stuff.

The sisters' biggest step into the spotlight together was at the Golden Globes ceremony this past January, as all three escorted presenters and winners off the stage as a collective Miss Golden Globe. It was way more fun than nerve-racking, they say—though Sistine's "heart skipped a beat" when Leonardo DiCaprio remembered having met her through her parents, Scarlet "fainted a little" when she congratulated Ryan Gosling and he smiled at her, and Sophia got "really bumbly" with Ryan Reynolds. "It just came out like word vomit," Sistine says as they all laugh.

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Victor Demarchelier
From left: On Sophia: La Perla swimsuit; On Scarlet: Sandro jacket; La Perla boy shorts; On Sistine: La Perla bandeau and boy shorts.

SUMMER STAPLES: Bumble and Bumble Surf Spray, $27, sephora.com; Atelier Cologne Clémentine California Cologne Absolue Pure Perfume, $130, sephora.com.

Their bond—as sisters and besties—comes through quickly as they get dolled up for this photo shoot at an oceanfront house in Santa Monica. Because while they're all stunning, slim, and tall, and dressed totally on trend, they're also goofy, funny, and warm, alternately complimenting and sharing embarrassing stories about one another. When the sisters admit how relieved they were that no one slipped onstage at the Globes, Sophia and Sistine quickly offer that Scarlet would have been the likeliest candidate. "She's very clumsy," Sistine teases. "I'm not used to wearing heels," Scarlet says in her own defense. "I'm like a giraffe."

The girls credit their parents for keeping their focus on family and a good education. Plus, they feel they were easy kids—"very hermit-y," says Sophia, which is probably why they don't have famous friends. Really, Sistine says, the most famous name in their phones is their father's. Which makes Sophia think of his phone and laugh. "When I was little I used to go through my dad's phone and take numbers." Like? "Like Liam Hemsworth."

"I called him," says Sistine. "He never answered."

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Victor Demarchelier
On Sistine: Lands

Their unique personalities fall a bit along birth-order lines. "They're all totally different," says their mom, who sat back fully at ease while they got ready. "But I expect them all to work hard and do well with whatever they're good at."

Sophia, the oldest and a sophomore at USC, is a rule follower and considers herself the most serious of the three. A communications major, she wants to start her own business. "I love being a nerd," she says. She's also super-protective of her younger siblings: "My mom calls me 'the hawk.'"

Sistine, the second oldest, is a senior in high school and has the driest sense of humor. She signed with IMG Models two years ago and has already had more than her fair share of pinch-me moments. Her first runway show? Chanel at the Ritz in Paris this past December, where she met Karl Lagerfeld during her fitting backstage. ("I don't think I've ever been so starstruck," says Sistine.) In January, she and Sophia both walked in Dolce & Gabbana's menswear show in Milan, while Scarlet, too young to walk, watched from the front row.

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Victor Demarchelier
From left: On Scarlet: AG shirt and jeans; Ray-Ban sunglasses; Le Vian and Pandora Jewelry rings; Nike sneakers; On Sophia: AG shirt and shorts; Ray-Ban sunglasses; Guess earrings; Pandora Jewelry ring; Nike sneakers; On Sistine: AG shirt; Guess shorts and earrings; Ray-Ban sunglasses; Nike sneakers.

SULTRY SHADES: Tom Ford Bronzing Primer, $74, sephora.com; Giorgio Armani Rouge Ecstasy Express Moisture Rich Lipcolor in 104, $38, sephora.com.

Scarlet, the youngest, is an eighth-grade track star and the most outgoing of the clan. Sistine swears that Scarlet could be a stand-up comic or have her own talk show. Scarlet agrees, but for now she's trying to get through school without another detention for talking.

Life chez Stallone is pretty low-key, with pool time and movies in their plush home theater; whenever one of Sly's films is on, Sistine reports, he makes his daughters watch, then discuss it. Their 70-year-old father captures much of their antics in videos that he posts on Instagram for his 2.7 million followers. "He brags about that," says Sistine, since she and Sophia each have around 360,000 followers. He loves to catch them off-guard, say, filming them as they wake up. "He'll be like, 'Hey, good morning!'" says Sophia, "and we'll be like, 'Thanks, Sly.'"

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Victor Demarchelier
From left: On Sophia: Moschino Couture dress and shoes; Simon G. Jewelry earrings and bracelet; Le Vian ring; On Sistine: Moschino Couture dress and shoes; Le Vian earrings and ring; Simon G. Jewelry bracelet; On Scarlet: Moschino Couture dress and shoes; Simon G. Jewelry earrings; Le Vian ring.

Rest assured, the girls get their payback by using Snapchat filters on their parents—"the ugly ones," says Sistine. "They still don't understand Snapchat." As much fun as the sisters have groaning about their parents, they are also grateful for their guidance. Their dad, for instance, famous for his mumble, made it a point to teach them to enunciate better than he does. "He would have us memorize poems," says Sophia. To this day, as she and Sistine demonstrate, they can still recite a good chunk of "The Raven," by Edgar Allan Poe. Even now, Sophia and her father regularly discuss poetry and art. "He's so smart," she says. "People don't realize." He also coached their daily fitness training. "We'd get up really early, like 6 a.m.," says Sophia, "and do 20 sit-ups and push-ups, practice our shot put—he wanted us to be really good at shot-putting for some reason—learn how to throw a punch, and practice golf." What did they call that intense morning ritual? "We called it an inconvenience," says Sistine, as drily as ever.

The siblings' beauty routines they've gotten from their mom. Most mornings they'll scrub their faces with glycolic cleanser, apply moisturizer, and top it with eye-cream serum. At night Scarlet also applies a spot treatment to her pimples. "Teens always get the worst acne," she says with a sigh. As for makeup, while Scarlet spends just 10 minutes before school putting on concealer and eye shadow, Sistine will take up to two hours on her face. With all the tricks she's learned on set, she's become the go-to makeup artist for her sisters and friends. Winged eyeliner? "I've mastered it," says Sistine.

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Victor Demarchelier
Clockwise from top: On Scarlet: J. Crew bikini top; Gabriel & Co. earrings; On Sophia: J. Crew swimsuit; Simon G. Jewelry earrings; On Sistine: J. Crew bikini top; Le Vian earrings.

FRESH FACE: Yves Saint Laurent Top Secrets All-in-One BB Cream Skintone Corrector, $52, sephora.com; Hourglass Arch Brow Sculpting Pencil, $34, sephora.com.

Going forward, there's one thing none of them plans to take from their dad: "I don't think any of us have the acting gene," says Sophia. She and Sistine make their little sister tell the story of the time she tried acting in the 2014 film Reach Me. "I literally just had to say one tiny line, and they had to cut that in half!" groans Scarlet. "It was pretty humiliating." Instead Sophia wants to start a makeup or fashion line. Sistine hopes to balance modeling with college. And Scarlet? She's not sure. "I'm still in middle school," she says, shrugging.

"This is all so new," Sophia says of this stage of their Hollywood life, "but we are so close." So close, in fact, that one time in Thailand, where their dad was filming Rambo, Scarlet got a haircut that was so short she cried, and Sistine came to her rescue in a unique way: "I said, 'Cut off all my hair too.'" And she did. Sistine grins. "I still use that," she says. " 'I cut off all my hair for you.' " Suffice it to say, if Hollywood takes any stabs at them, they'll have one another's backs then too. Sure, adds Sophia, "sometimes siblings can get into rivalries, but we've been nothing but support to one another." And if a conflict comes up that they need to settle? They have just the tools to battle it out.

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Victor Demarchelier
Clockwise from top: On Sistine: Ermanno Scervino dress; Le Vian earrings; Simon G. Jewelry bracelet; On Sophia: Ermanno Scervino dress; Le Vian ringl Simon G. Jewelry bracelet; On Scarlet: Ermanno Scervino dress; Simon G. Jewelry earrings; Le Vian ring.
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Amy Spencer

Amy Spencer is a Los Angeles-based author, journalist, and happiness expert.