i really don't know when your parents and brother后为什么接would come bank而i really don't know when your parents and brother后为什么接would come bank而不是will come back

i really don't know when your parents and brother后为什么接would come bank而i really don't know when your parents and brother后为什么接would come bank而不是will come back
i really don't know when your parents and brother后为什么接would come bank而
i really don't know when your parents and brother后为什么接would come bank而不是will come back

i really don't know when your parents and brother后为什么接would come bank而i really don't know when your parents and brother后为什么接would come bank而不是will come back
是虚拟语气,类似can,will的词在情况不确定是都会使用虚拟语气

选择B ，A多在口语中。 B有虚拟 也表猜测很重（实在不知道什么时候回来），结合主句看B的感情更浓，选A感情语气过于平淡（似乎知道妈妈哥哥要回来），B（实在不知道什么时候，一点概念也没有）

译：我实在不知道你的父母和哥哥什么时候会回来