In 1994 journalist and music critic Mikal Gilmore , the younger brother of convicted killer Gary Gilmore, wrote a somber, searching memoir, Shot in the Heart, about what it means to come from a family with violence running through its veins. It’s a haunting book, and not an optimistic one. Can the capacity to commit horrific acts be passed through bloodlines? And how, if at all, can the chain be broken? That’s one of the questions Aleshea Harris asks in her lively, ambitious, darkly funny debut Is God Is, which she adapted from her 2018 play. Racine (Kara Young) and Anaia (Mallori Johnson) are twins who cling to one another: A childhood tragedy that marked them both emotionally and physically has caused them to retreat into a universe of their own making. Anaia’s face is a network of scars, the result of devastating childhood burns. Racine has scars too, but they’re less immediately noticeable, mostly visible on one hand.…