In April 1981, four of Fernando Valenzuela’s brothers — Daniel, left, Avelino, Francisco and Manuel Valenzuela — visit the field in Etchohuaquila, Sonora, Mexico, where they learned to play baseball. “It’s hard to believe, no?” El Zurdo — “The Lefty” — would be Fernando Valenzuela, the youngest of 12 children from this desert hamlet in northwest Mexico who would corral …