父母本来是3月回国的，现在航班取消，申请改成4月的返城机票。就为了这一个月，现在要申请延期。
1. 准备邮寄B2延期申请。是申请人填写I529，标注副申请人;副申请人还需要填写I529吗？-No, but 副申请人need to file/complete I-539A and send it together with I-539. Only need to pay one I-539 filing fee plus 2 biometrics fee.
Read this link: https://www.uscis.gov/i-539
2. 因为是邮寄申请，是交一份申请费加两个biometric fee吗？就是$370+$85x2=$540-Correct.
3. 父母是4月就回国，估计到时候延期批准还没有下来。现在有biometric，看USCIS网上说到时候不去打指纹就直接拒了B2延期。可父母走时估计也收不到打指纹的通知。
-As long as they get the I-539 and I-539A filing receipt notice, they can leave US. Thye can bring the receipt notices with them when they come to US again.
这样不是延期就被拒了，而他们多呆了一个月是逾期。10年签证是不是就作废了？
-Yes.
