I think the reason they didn't give people who were still alive was because that, if those others popped up somehow, people would get suspicious.

So they just picked 3 people randomly that had died. I don't think there was much thought to it. And IMO those 3 were the most innocent and press-friendly people because they were pretty clean cut individuals (at least Boone and Libby), while Charlie was a celebrity. So yeah. I don't think these 3 have much to do with the plot.

I think they felt the need to include these 3 was because it's pretty improbable that all 5 of the people that got off the plane were able to survive. All of them? It's very doubtful.