请教8老师，公婆一个B1，一个B2，能一起申请延期吗？

两个人都是10年B1/B2 Visa，目前要申请延期才发现I-94上一个B1，一个B2，这种情况下，能一起申请延期吗？就是一个人填写I-539，另一个人填写I-539A，这样的话，邮寄交一份申请费$370就可以了。
我看I-539的Instruction写的是：
You may include your spouse and your unmarried children under 21 years of age as co-applicants in your application for the same extension or change of status, but only if you are all now in the same status or they are all in derivative status.
想问问B1、B2是不是derivative status？
多谢8老师了！