Bess Wohl’s new comedy Make Believe portrays a quartet of Gen-X siblings at two points of life-changing family crisis. The first is in 1980, when the Conlees, two sisters and two brothers, are small children. The second is 32 years later. In both instances, the kids are gathered—it’s tempting to say “barricaded”—in a gargantuan nursery at the top of their parents’ luxe suburban home.