None of that explains why Sisko couldn't talk to Jake or Kasidy and treat them like adults. That he couldn't give them a reason why he felt the need to do what he did.
RBoE seemed to be pretty clear that Sisko was using procrastination as a defense, to try to avoid directly confronting the issue more than he had to. Cowardly? Sure.
I don't think the book stated that their deaths were certain, only that Sisko felt something bad was in the offing. I might be wrong on that account, since I read the book over a year ago and a lot of details have been forgotten.
Sisko told Kasidy in his message back that the bad things were getting closer to home, the examples of bad things he gave being of people who were killed or, at best, suffered irreversible brain damage. I think we can assume that he believed the deaths of those he loved to be in the offing.
Nor does it explain why he left his family to plan Joseph's funeral.
Joseph's funeral occurred after the Borg assault on Alonis (among other worlds), just before he met with Akaar to get a ship, and perhaps a week before he returned to Bajor where Kasidy kicked him out. You've got the sequence wrong.
I meant he left his family on Earth, his sister, etc, to plan Joseph's funeral instead of being a part of that himself. That was another thing that felt out of character to me. Sisko's strong relationship with his father, seeing the restaurant as a refuge, was well established on the show. And there had been nothing in the literature even to suggest that had changed, until Rough Beasts.