Kendall Jenner just celebrated her 18th birthday, and while thankfully there have been no media mentions of a lurking or orchestrated sex tape, the reality star and model celebrated the occasion in Kardashian style: a risqué, breast-baring, “all grown up” photo shoot.

Even though that catapulted Jenner into the entertainment news headlines, she received far greater press attention with a conveniently paparazzi-swarmed dinner date in Los Angeles last week with international dream boy Harry Styles of the British boyband One Direction. So as their older siblings – Kim, Kourtney and Khloe – focus their attention on marriages and motherhood and no longer seem to have the appeal they once did, is it now up to the younger two – Kendall and Kylie, 16 – to carry the torch and keep the family flame, fame, and fortune prospering?

PHOTOS: Click here for more pictures of Kendall and Kylie

“The Jenner girls are being groomed to become their own brand, under the Jenner name. While of course they are playing up to the Kardashian family ties, they are different brands than the [older three sisters],” Ronn Torossian, CEO of 5WPR and author of “For Immediate Release,” told FOX411.

“While the Kardashian sisters are all committed, with Kanye West in the picture and perhaps a divorce [in] the cards for Khloe and Lamar Odom, the older sisters are fading from the spotlight quickly.”

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But there are few in the entertainment industry who would argue that Kris Jenner has everything mapped out. The momager personally took charge of her offspring’s careers several years ago and made them multimillion-dollar names out of next to nothing – as well as making herself quite a well-known name in the process. Now we’re told that Jenner has been positioning her youngest two for success for quite some time.

One inside source said mom made sure her daughters were known and introduced to MTV executives during a Kim Kardashian-focused project in New York a couple of years ago, and that she seemed particularly selective of what jobs Kendall – who is long and lean and stands at the perfect model height – took on as she established herself in the fashion business.

“Kendall is headed for Vogue,” the source said.

Indeed Kendall’s controversial fishnet-wearing, topless photo was taken by famed Vogue snapper Russell James and was accompanied by tweets from Khloe praising the “high fashion” look.

And as we have seen, particularly in the case of Kim, who has previously dated the high-profile likes of rapper Ray J, football star Reggie Bush and now Kanye West (her marriage to the lesser-known basketball player Kris Humphries lasted a grand total of 72 days), star-studded relationships are of crucial importance. So it should not come as a surprise that Kendall was snapped with Styles, and that the same week Kylie was photographed shopping affectionately with her rumored beau, Will and Jada Smith’s teen son, Jaden.

Yet some critics are doubtful that Kylie and Kendall – who both boast a net worth of around $2 million and have upwards of 6 million followers on Instagram and Twitter – have the dynamism to take Kardashian-ism to the next level.

“We’ve seen again and again how many brands on a [downward] slope in popularity introduce new products. Not all humans are brand dynasties – the Jenner girls’ campaign is another attempt by queenmaker mom/manager Kris to hang on to the throne,” said Alex Shvarts, CEO of online branding agency Simply Mint. “They will need individuality and ongoing marketing. The blitz and fluff will subside soon enough, and if by then the Jenner girls have not built a core solid audience, they will disappear as quickly as they appeared.”

And it seems the young girls are taking advantage of the enormous paychecks that come with promoting products via social media, though their hawking routinely seems to irk followers, given how disconnected they often come across. Last week Kendall tweeted everything from “Staying true to my LA roots with my favorite @pacsun shirt” to “Kylie & I are considering a career at @VirginAmerica” to “Using the #covetfashion game to create a look for tonight!”

“Please go away,” one follower tweeted. Another referred to Kendall as “the most annoying tweeter in the world, and like a 13-year-old on MySpace,” while others concluded that “the Jenner and Kardashian family are so spoiled and annoying” before questioning “why people even look up to them.” Scores of others, meanwhile, said the girls had succumbed to the dreaded “overexposure.”

But others beg to differ when it comes to their ability to make their goods last long-term.

“At this point, it is certainly working for Kylie and Kendall, they are both relevant because they are becoming household names,” Torossian said. “But based on their current trajectory, the Jenner girls are being positioned to have a long-term career. Let’s not forget, their dad Bruce was a celebrity many years ago and Kim is a brilliant marketer and has a great brand. The Jenner girls would be wise to pay attention to their sisters’ career paths.”