Related Posts & Category Page Question

I am redesigning my site using Divi Ultimate Child Theme (https://waynestocks.com/photos/sports/photos-2021-01-30-basketball-at-johnstown/). I have the same question related to both related posts and Category Pages. I would like them to include all entries from the Parent Catagory rather than be limited to only those in exactly the same subcategory. For example (and there aren't a lot of example posts yet), I would like the related posts to draw from all posts under the Parent Category "Photos" rather than limit it to "Sports" if that is the subcategory of the post. Likewise, I would like do away with the subcategories in the menu and just have a link to a category page that would include any post with a subcategory under that parent.