I am sorry that your birds died. But accidents do happen. Nobody on this forum wakes up thinking: "Today I am going to kill my birds." But sometimes things go terribly wrong.
I know the feeling of constantly being afraid for their health. I took my Schnappi to the vet all the time. I was always hoping the vet would say: "It is nothing, the bird is healthy." Unfortunately, it was always something.
I think it is normal for you to be somewhat paranoid after all you have been through. It will be a while before you can relax again,