BEIJING  - China’s one-child rule has numerous critics, but perhaps none have so emphatically defied the policy as a couple who have accumulated four boys and four girls - some born to two surrogate mothers. Authorities are calculating how high a fine to impose on the family, described as “rich merchants” in Guangdong, state media said, estimating that it could reach 10 times their annual income. “A high fee will be imposed on the parents,” the Southern Daily reported, citing local family planning and health officials. “The investigation into the case is basically complete.” The one-child policy was imposed three decades ago to limit growth in China’s population, now the largest in the world at 1.35b, but critics say it is no longer needed.