I’m so sorry. With horses, you try to do everything right, and sometimes everything still goes wrong.
One piece of advice I will offer, though (and take it with a grain of salt): you may want to re-evaluate your horses’ living situation. It sounds like they were boarded. So many boarding barns contribute to an unhealthy/unsound lifestyle for reasons too numerous for me to list.
I know you’re feeling rather gun shy, but when you get your next horse, you may want to try to find/create an ideal living situation first, then bring in the horse.
Please feel free to disregard my thoughts if they do not apply. Also, I want to stress I’m not trying to place the blame on you or even the boarding barns. We are all influenced by 21st century forces that make horse keeping a challenge. Even in “perfect” situations, horses aren’t immune to issues. Yet amid such a string of bad luck, it may be a consideration to break the cycle.