邮件里的句子We are yet to finalize all the user stories and Joanna is swamped with ＸＸproduction work.
be yet to的用法：http://www.englishforums.com/English/BeYetToDo/xddbk/post.htm
"Yet" means "still", or "remaining," in this context.
This remains to be done.
This is still to be done.
This is yet to be done.
What is there to do?
What is [there] yet to do?
This is yet to do.
As you can see, the question works better than the statement, unless you use the passive.
None of these are really common.
I hear "She has yet to do something/anything worthwhile." (So far, she hasn't done anything worthwhile.)
例２：Police were yet to confirm whether..
"To be yet to" means that they are working on confirming the details, but they haven't yet.
Here's an example:
"I have yet to meet another person who has read the book by John Smith."
It almost implies that I'm actually looking for someone who has read the book, but I just can't find anyone.
It could also be written in these ways:
"I have yet to meet anyone who has read the book by John Smith."
"I haven't yet met anyone who has read the book..."
"I still haven't met anyone who has read the book..."
I hope that I haven't confused you more!