It's not quite accurate to call this the "new" film from the Duplass Brothers.
That's actually "Jeff, Who Lives At Home." Or "Kevin," a documentary that they also recently finished.
What happened here is that before "Cyrus," the Duplass Brothers directed this film about what happens when two brothers let something fester, unfinished, and then they ran out of money and time to finish it, and so it festered, unfinished. And now, finally, they've gone back and completed it, and the result is a charming, low-key look at brotherly competition and the ways it can twist an already complicated dynamic into something sour and painful.