Is that what you and your sister do?句子正确吗？

是正确的~
是复合结构
That is what you and your sister do.
what 引导的表语从句

对啊
That is what I and my sister do.
最好后面改成名词
这是个表语从句
what I and my sister do做表语

正确，是复合句。
That is what you and your sister do.
what引导表语从句
汉语意思是“那是你和你的姐姐所做的一切吗？”

错的!!!!