Gee, that's a horrible thing to find at any time. On top of the grieving you are already dealing with, your emotions are really being put to the test.
Some people just aren't as responsible as other people, no matter what age they are. I suspect you do a lot of things for him and his daughter, that he would have to do himself, if he wasn't living with you. Actually, that might have been part of his problem. Was he having to do other day to day things for himself and for her, that you usually do? If so, then the chickens may have just gotten lost in the shuffle or not been as high a priority, as the other things he was trying to do and keep straight.
Honestly, I think a lot of chickens have been lost to people that have never had a predator problem and leave the coop open for some reason, for "just one night." They aren't thinking, "I'll leave it open, I don't care if they get killed." They really don't think it'll be a problem. As for the noise, I think a lot of people have slept through attacks.
Whatever the reasons for what happened, I think you are very wise to understand that you need to find a way to work through this and get past it, without doing damage to yourself or your family. When you live in another person's home, there isn't much that is your personal space. Although you may not have felt like entrusting him with your incubator, I think it was a wonderful thing that he was offering some of his personal space for it. I can't fault him for feeling worse about how this effected you, than about how it effected the chickens. He loves you more than he loved the chickens. Look what you've done for him, opening your home to him and his child. If you could turn back time, I'd like to think he would have done a better job. I really don't think he was anticipating this course of events.
In the future, a list of things to be done and an evening call to check on things sounds like a good plan, just to make sure things are alright. I think you came up with a good idea there. What happened to your chickens was terrible, but it happened. All you can do is work through your own emotions, wait for time to heal them a bit and plan for a better future. I hope you have a really great hatch!