A Swiftly Tilting Planet

This is the third book written (although the fourth book chronologically) in Madeleine L'Engle's Time series. I would say I enjoy it more than Many Water but not as much as either Wrinkle or Wind. As with all the books in the series, the actual story mostly serves as a vehicle to explore an interesting issue. In this case, Charles Wallace travels throughout time but always staying in the same place and experiences a series of interlocking stories. The big picture to me is the way that brother-against-brother (both literal and figurative) conflict has happened throughout time, and the outcomes of those conflicts have ripple effects. The through-line story is hard to follow because so many of the characters have purposefully similar names, which illustrates their ties but makes it hard to keep track. I also was aware in this reread more than I have before of the Indigenous people L'Engle portrays in the book. I'm curious if they were based on an actual tribe that L'Engle had researched (I can't find any information on the web on this), or if they were just a people group she imagined. Although they are respected and important people in the book, I'm concerned whether the portrayal is accurate or respectful.