Movie siblings can make or break the believability of a feature film. Cast two actors who can convincingly play family members, and you're in the clear; cast two actors who look nothing alike, and you're in trouble.
Thankfully, "The Five-Year Engagement" falls in the former category. In the film, actresses Emily Blunt and Alison Brie play sisters, and not only do they look alike, but they sound alike too. (This is quite a feat since Blunt is British and Brie is not.)
"I had a great vocal coach here in LA for a few weeks, but when I got out there, Emily became my unofficial vocal coach," Brie said last year to The Insider. "It was more important that we sound alike than me studying a super proper British accent." Mission accomplished, Alison!
In honor of the success of "Five-Year Engagement," HuffPost Entertainment has compiled ten other great sibling pairings from the big screen. Leave your own favorites in the comments below!
The curly hair. The squinty eyes. The expert stupidity. Ferrell and Reilly may have played stepbrothers in "Step Brothers," but they could have easily been actually related.
Natalie Portman played Anne Boelyn. Scarlett Johansson was Mary Boelyn, the other Boelyn girl. These two don't look related, but who cares? Yes, who cares.
Wahlberg and Bale played half-brothers in "The Fighter" and their shared bombast -- and Bahstan accents -- made them feel like family.
Emily Blunt: the best big-screen sister ever? In addition to believably sharing relations with Alison Brie in "The Five-Year Engagement," she played Amy Adams ne'er-do-well sis in "Sunshine Cleaning." She also looks like Rosemarie DeWitt, who stars as her sister in "Your Sister's Sister." Only question: when will Jenna Fischer play her sister?
Perhaps the best onscreen sibling pairing: not only do Anne Hathaway and the aforementioned DeWitt look alike, they also seem to have that familial bond.
In the unconventional indie dramedy "The Kids Are All Right," Hutcherson and Wasikowska share the same dad (sperm-donor Mark Ruffalo) but have different moms (committed partners Julianne Moore and Annette Bening). The casting isn't that great -- after all, these two don't really look alike beyond having giant mouths -- but they're so adorable it doesn't really matter.
Cameron Diaz and Toni Collette: You wouldn't think they look alike, but then you realize they kinda do? At least enough to play siblings.
When "Zombieland" came out, Emma Stone and Abigail Breslin didn't really look all that similar. As Breslin has aged though, the resemblance grows. Kudos to casting director John Papsidera for spotting the potential early on! [PHOTOS: Getty]
In the drama "Brothers," Tobey Maguire and Jake Gyllenhaal play brothers (no kidding, right?). The casting takes advantage of the fact that these two look so much alike that "Spider-Man" producers almost replaced Maguire with Gyllenhaal during a contract dispute between the first and second films. [PHOTOS: Getty]
No, they don't look anything alike, but it's Hollywood. Look for "Triplets" -- which will cast Eddie Murphy as the pair's third brother -- in the near future. (Not a joke.) [PHOTOS: Getty]