I also have been intrigued by this thread and re-read it. So, first of all, thank you for sharing this interesting challenge.

I think Sue has made a key point about the likely speed of travel and the mindset for such a trek. This is more a slow migration, meander thing than a sprint, summit-fever stampede.

To me this raises two areas of concern: first, you are going to have a lot of living to do along the way, and second, endurance and finishing are the primary goals.

You should consider what makes living worthwhile, even fun, for your family and prepare to meet those wants and needs. I imagine many opportunities to teach life lessons to any children; maybe each child will need a lesson plan to consider most days along the way. Morale will be a big deal: a few presents /suprises, especially if a birthday or holiday or two can be anticipated to occur.

Add some stuff aimed at ensuring endurance. Mechanically, spares crucial to walking come to mind; repair tools and supplies for such things make sense. Psychologically, as a leader you may want to set the tone that you are going to get home, it is going to take a while, and needing to relax and take it day by day. Rest days, regularly and whenever butts are dragging, as well as celebrations are going to make sense. Perhaps your spouse could be morale officer.

You are going to want alternate route information for both sides of the river. Hopefully, and I would expect, most of the journey will be boring slogs along intact road or railroad. At each point where that is impossible due to earthquake damage, you want to find a safe way around even if it means backtracking a bit. Plan to make the kids to complain about being bored and tired, not scared.

If not taking the on-the-water option, then the biggest problem would seem to be spots where you must cross the river to get to the road and railroad. In such places, I would take a very hard look at staying on your side of the river instead, even if it means slower going.