-Depends on which province issued their passport and their户口所在地. So, it is 内蒙.
父母到北京签证面试后就想直接回海南了。签证后是不是大使馆将护照收走,印好签证后再邮寄给他们?
-Your parents can pick it up after they get the visa (may wait for a couple of days, check US Enbassy website). Your parents also can ask the passport to be sent tothe address in 海南.