Here "Now" is used to mark a pause in the story. Matthew tells background information about why the crowd chose Barabbas. (See: [[rc://en/ta/man/jit/writing-background]])
The phrase "ask for Barabbas" is an ellipsis for "ask Pilate to release Barabbas." The phrase "destroy Jesus" here is a euphemism for "kill Jesus," and because the people in the crowd would not kill Jesus themselves, it is a metonym or ellipsis for the crowd telling Pilate to have his soldiers kill Jesus. Alternate translation: "they should ask Pilate to release Jesus and tell him to have his soldiers kill Jesus" (See: [[rc://en/ta/man/jit/figs-ellipsis]] and [[rc://en/ta/man/jit/figs-euphemism]] and [[rc://en/ta/man/jit/figs-metonymy]])