The twins are played by Mark and Michael Polish, who are also responsible for the script. Michael - in an act of impressive multitasking that shows up even the behind-the-camera Coen Brothers - also directs. They're the timid sort, showing little but resigned acceptance when Penny makes a quick exit. But she's drawn back to the twins through a mix of necessity and curiosity. When Francis falls ill, Penny becomes ever more attached to the twins, and they all begin to confront their loneliness and inner demons.
While mostly shot in a very stylised manner, early quirk quickly transforms into genuine emotion. There are still eccentric characters who pop-up every now and again (and the two-dollar reappears in the final act to provide some heavy-handed symbolic insight) but this is a film that surprises with constantly raw, vivid and engaging emotional energy. Blake and Francis don't always say much, but we really learn to care for their characters. With no-one to reliable on but themselves, their journey is a fascinating one. The inherent problems of two individuals conjoined are examined in some depth, but it's mostly just a way to examine the complex nature of family relationships. How autobiographical the film is is certainly cause for conjecture, but this is certainly a thoughtful portrait of brotherly affection. There's only one unusual make-up shot showing the physical 'binding' of the brothers Falls, but it's that bond that defines every frame of the movie.
The story structure isn't the most original, granted, and the stylisation doesn't always work (although I must reserve praise for a 'climactic' - however meaningless that word is in this case - flight of silent psychological fantasy that really hits home, despite seeming somewhat out-of-place). But Twin Falls Idaho calmly drifts towards some hugely satisfying emotional payoffs. It's to the Polish Brothers' credit that we're so invested in the characters they've created that we generally care for their well-being by the film's concluding chapters. Poignant without resorting to cheap sentimentality, Twin Falls Idaho is flawed but so full of charm and warmth it's very hard to resist.
An aside: I do express mild disappointment that they missed out on this music cue. I guess it wouldn't have made any sense at all. But still.