Hi,
I have been discussing your issues with some my colleagues in WordCamp Contributor’s Day and would like to help you.
I would like to suggest you to use this plugin on the page
https://wordpress.org/plugins/wp-recent-posts-from-category/
This display recent posts by category
It can be used in any page or post or widget.
If you need in the widget the page should have widget container.
ie sidebar configured in code and shortcode can be added from widget backend.
If needed in home page, the short code should be added in the page that home page uses
or the template that the post or page uses.
Regards
