I'm so sorry for your loss. Losing a little feathered friend is the most gut wrenching feeling in the world. The 'should haves', what ifs' etc, drive us crazy. It does me...even after two and a half years of losing my Amazon. My life will never feel the same. It's because we love them so, and we are trying to make sense of everything, but in reality terribly sad, life changing things happen. Birds are very fragile but it is clear your birds have a loving, caring home with you. As much as we do to keep them safe it is actually impossible to keep them safe from everything.
We have to remember the joy they gave, and how happy they were living with us. Also, how amazing that we shared our lives with our birds. That, in the millions of years that earth has existed, we were living on this planet at exactly the same time as them. I personally am SO thankful for that. I find that thinking happy, positive memories of them, helps to get through the horrible thoughts.
My thoughts are with you at this sad time.