Roundabout Theater Company is promoting from within, tapping its well-received small-scale production of “Bad Jews” to move up to the org’s larger Off Broadway space for a run that begins in the fall.Josh Harmon’s “Bad Jews,” about two cousins fighting over an heirloom of their late grandmother’s, was initially produced last year as part of the Roundabout Underground series, the theater’s programming dedicated to smaller productions that are showcases for emerging creatives. Play’s original cast — Tracee Chimo, Philip Ettinger, Molly Ranson and Michael Zegen — will return for the move to the Laura Pels Theater, as will helmer Daniel Aukin. The Underground series has previously yielded another Off Broadway title, Pulitzer finalist “Sons of the Prophet” by Stephen Karam, whose first play was produced in the Underground series. Roundabout also has set the sked for its latest series of Underground readings, of which “Bad Jews” is an alum. Writers on the docket include Jonathan Caren (“The Recommendation”), Rachel Bonds (“Swimmers”), Mat Smart (“Tinker to Evers to Chance”), Christian Durso (“Shiner”) and Kate Gersten (“Benefit of the Doubt”). Reading series runs Feb. 25-March 1. “Bad Jews,” meanwhile, gears up for a run that begins Sept. 20.