Hmmm, wp_list_categories has a tag that lists children, but only children of the current page — in other words, not siblings.
So I’ll move to Pages to solve most of the problem.
This is what I’m going for now:
Page A
> Page a-1 (shows a-1 and a-2 as subnavigation)
> Page a-2 (shows a-1 and a-2 as subnavigation)
(a-2 is assigned to category z)
list of post titles of category z
> full post
– each indent is a level, so click on A and see a-1 and a-2
– a-1 and a-2 will always display links to each other (they are subnavigation in this A section)
– Page a-2 displays post titles of category z
– click on a post title to see the full post
I’m hoping to have this automated, so if new a-X Pages are added, they automatically appear in the subnavigation. And as new posts are added to a category, they automatically appear on the assigned page. I also want to automate the templates so I don’t need a unique template for each category — new categories should automatically follow along.