My concern is not to protect him or justify what he did, but since most of the party was eliminated then all we can do is try to help the ones who are still around, the kids and if needed some mental help for the father, you can't deny that a guy who kills his family is something you hear of very often, so we must consider the possibility of some underlying factors.
And why do you think the kids will grow up blaming themselves? You watch too much TV me thinks...
What's going on in my head is the curiosity of what was going on in his, if we don't discover why he did this then we won't be able to find the factors of his life that led up to the event and thus allow us to prevent this from happening in the future.