Epics typically involve tragedies. How can they not? While the arc of history may bend toward justice — and at times, that “may” feels mighty wobbly — the cadence of history visits catastrophe on so many in the meantime. Italian playwright Stefano Massini’s “The Lehman Trilogy,” about the siblings who founded the Lehman Brothers investment bank, is epic in length (it runs a hair over three hours; Massini’s initial version was closer to eight) and Homeric sensibility. Matthew Boston brings verve and heft as Henry Lehman, the first of the enterprising Lehman brothers to arrive from Rimpar, Bavaria.