I am not sure what you want. Your thread asks for help understanding Family week at rehab but your post indicates that you are far from ready to have her come home.
First, Family Week varies from rehab to rehab, perhaps the rehab itself can give you more information about how it works there. Often it involves family counseling and sharing and sometimes puts a plan in place for "after" rehab. They can tell you best.
Your post indicates that you have a lot of responsibility already and are not ready for her to return and go through this all again. The thing is, there are no guarantees with rehab and that is often what happens.
I think setting your boundaries, about what works for you and what does not, and deciding how you will enforce them or if you are even prepared to do that, should she cross the line, is important.
You don't want to leave, but wishing things were different or even insisting that things BE different is not going to change the outcome.
For everyone's sake, I hope she comes out of rehab after full completion and stays clean and sober the rest of her life. Really truly, I do wish that for all of you. I just think you need to prepare yourself for if it doesn't go well.
Congratulations on your own recovery. Your children need you to stay strong and keep them safe.
Good Luck