Hello hello! Have added you here. I have selective mutism and have written about it some (check the tag if you are interested). I'm glad to answer any questions via textual format. These books are definitely the best representation I've found... but I did not love all of them. The 3rd book has some Native American appropriation (of a costume, which is a plot point).

When I tried to read #5 this last winter, I just couldn't get into it. Maybe I was not in the right mood.