Sibling Rivalry! Models Amelia & Delilah Hamlin 'Trying To One-Up Each Other' When It Comes To Their Celeb Boyfriends

Just call it a sister act: Judging by all their cuddly selfies, you'd think Amelia and Delilah Hamlin are thick as thieves. But behind the scenes, the girls are anything but chummy, an insider tells OK!. 

"They've been competing with each other for years, and now that they both have celeb boyfriends, they're convinced the other is trying to hog the spotlight," spills the insider. Ever since Amelia, 18, hooked up with Scott Disick, 37, last fall, Delilah's "annoyed because her sister's getting way more attention than she is," dishes the insider, noting that the blonde beauty, 22, has been dating Love Island's Eyal Booker, 25, for more than two years. 

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"Now, whenever Delilah packs on the PDA with Eyal, Amelia feels like she's doing it for attention," adds the insider. "If they keep trying to one-up each other, things could get pretty raunchy!"

"They push each other's buttons," the insider said of the daughters of Lisa Rinna and Harry Hamlin.

Meanwhile, Disick and Hamlin have been together for around three months — from the time they were spotted together at a Halloween party. And now, their romance seems to be getting serious — as OK! previously reported, the two are smitten with each other, and Hamlin is "so different" from anyone Disick has ever been with.

"Scott does everything he can to make Amelia happy," the insider noted, adding that Hamlin is beautiful, funny and self-confident, and Disick really finds it irresistible.

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The well-placed source even dished that Disick may want to take the next step. While together in Mexico, the source claimed "Scott did a shocking thing and proposed to Amelia." However, the insider cautioned that the proposal "was in the heat of the moment. So no one knows if it'll actually stick or not." 

Only time will tell where their romance is headed...