A warm welcome back, tttaylorrr. I remember that I was dealing with mites on my second BP around the same time that your battle with the mites started, and it actually gave me comfort and reassurance to see your can-do approach to such a stressful thing, since I have a lot of respect for the kindness and readiness to help that you've always exhibited in your posts. Since I took a similar approach (PAM for the enclosures, a spray for the snake itself - although I used the Natural Chemistry salt solution spray instead of Frontline) and things turned out okay, it was heartbreaking to read about what had happened with your two little ones.
I genuinely believe that you were not at fault for following several mainstay mite treatment guidelines to a T, but am glad that you gave yourself the ample time needed to heal from your grief and the feelings of guilt - often disproportionate, and yet unavoidable - that came attached with it. It's wonderful to hear that all your current snakes are doing well, and that speaks for itself as a testament to your dedication to them. It's great to have you back.