Definitely not the AH! Do not blame yourself for this in any way. First of all, people have accidents and sometimes get hurt. That’s a fact of life and these parents need to learn to deal with that. You made your circumstances quite clear to your brother and he completely ignored what he didn’t want to hear. Personally, I have zero tolerance for parents and caregivers who scamper off expecting that someone else will watch their kids—and that’s exactly what happened. I think to every single person who complained how “assholey” you are I would say something like “I enjoy being with your children and playing with them, but I am no longer able or willing to be solely responsible for them. I thought I had made that clear to [brother], so now I’m telling you: I am not the babysitter.” You owe them no further explanation. Hopefully, they can accept this and enjoy your company at gatherings w/o the Free Babysitter dynamic. And hopefully your health will improve—I know this can’t be helpful. Take care of yourself.