Putting on Shakespeare’s Hamlet and George Bernard Shaw’s Saint Joan with a cast of four people started as a way for fledging New York theater company, Bedlam, to keep their costs low. The gimmick paid off and five years later, they’re still performing the plays to rapt audiences. This week Bedlam comes to the Broad Stage, so we asked Artistic Director Eric Tucker how four actors become more than twenty-five characters, how the company got their evocative name, and why their productions stand out.