I share your concern for material that is at once all-ages and historically accurate -- not always an easy thing to accomplish when it comes to Civil War narratives!
While I position the FREEMAN COLBY books as YOUNG ADULT level, I consider them to be all-ages -- with the caveat that they're all-ages for all readers who are old enough to be interested in a survival story set in a historical time period.
I bring these books into my residencies at public elementary schools (grades k-8+) & have always encountered enthusiasm from teachers, students, & families for this particular method of handling challenging historical material. The stick figure style leaves much to the imagination; it also allows readers to bring their own level of understanding to the story.
That said, there IS some content depicting 19th century political and racial attitudes and norms that are, well, typical of the 19th century. I've altered a couple racial slurs in the original source texts, so as not to distract a modern reader from the overall story. (In my experience, any reader who is old enough to make it 300+ pages into the story, is also ready for a frank discussion of the historical attitudes of the characters.)
Also, for what it's worth, I have given copies of these books to my niece & nephew (ages 7 and 4). They aren't yet old enough to get all the historical connections, of course, but they have taken the art & storytelling to heart, & even started drawing their own comics in a similar style.
At any rate, you can read through most of VOLUME 1 on my "Live Free And Draw!" site here:
That's probably your best way to evaluate the story for your own reading family.