Jeannie, I hope you can find your way out of those feelings of guilt. You have nothing to feel guilty about where lack of testing is concerned. What you have given your children through this curiosity-led learning journey is likely to have far more impact on them as good human beings than any test they'll ever take in school.
We too have been unschooling our daughters (now 10 and 8) for the past 3 years. Our oldest wants to go to Performing Arts high school later on, and I too think about testing and other school-y stuff from time to time. But, I also pay attention to who my daughters are becoming, and how they learn. I am certain that you have paid some attention to how your daughters learn (right?), and can probably find online and local community resources such as test-prep websites, tutors, online programs, etc., that will bring your daughters up to date on what they're expected to know at the 5th (and 7th) grade levels.
Whatever your daughter doesn't yet know, she can surely learn. Find out what's required, and ease your daughter into the potential school space by getting her familiar with the information. Proficiency is a process, and she doesn't have to ace any tests. She just has to be familiar enough with the material and expectations to do alright. Once she's in, she can gain her footing over time.
I send you love and light as you sort though this process. Above all, just remember that you're raising people who are probably pretty good at figuring out how to get what they need. This experience is about a partnership with you and your daughter(s); you are not more responsible for this enrollment process than the daughter who wants to go to school. She is choosing this, and so she is in part responsible for readying herself to enter school. You are her helper, and as such, you can help her find resources to practice. But she is responsible for studying and preparing, not you. You're in it together, and I think you'll both be alright.