Hi Ernest,
Point 1.
The collaborators who manage our WP site say that following your indication, we will get this scenario:
Flagging one Parent and two or more child categories of it, the system will display the posts which belong to both the child categories, as long as these posts have been categorized with both the child categories.
If the post belongs only to one of the child, it will not be displayed.
If this is true, is not what we are looking for, usually, posts belong to only one child category.
Ex
Parent: YEAR CYCLE
Child: Pesach + Shavuot
Result: posts tagged as Pesach + Shavuot at the same time.
Best Regards,
Rosa