Could these cats be saved? If so, how?

It's sad, but sometimes life just "happens". There are outside forces that we cannot control, that's just the way life is. I understand you completely, when I was 16 I found a kitten outside, my boyfriend and I took him in (I lived alone at the time believe it or not) and honestly we had one great year with him. He was the sweetest cat, we loved him soooo much. One night we went to bed, he slept with us on our bed like every other night and in the morning (not even four hours later) I woke up and found him hanging from my mezzanine (I'm not sure what it's called in english but it's essentialy a half floor in a loft) He some how got his collar stuck on some Christmas lights and fell. For years I wondered what I could have done.. maybe if I haden't put the Christmas lights up or if I didn't make him wear a collar he's still be alive but the reality is I'm not psychic and there was no way I could have prevented it. I still go to bed some nights and cry about it.. and I'm 25 now.. but in my heart I know I gave him a good life while he was alive and I've made peace with what happened. The same should go for you. We're only human, life is not like the movies where minutes before someone we love dies we have an epiphany and just in the nick of time save them. You did a good thing trying to give them a good life, unfortunately life had other plans but in your heart you should always remember while they were alive you gave them the best life possible.