Regarding the first issue, the featured image size for those posts seems to be coming up smaller than the recommended one. So, can you upload the featured images of the posts in your site of size 800px * 600px or greater than that one and check for the same? And regarding the screenshot, you can provide the url to screenshot in the forum thread.
Also, I could see that every widget added in your site is displaying 5 posts within it. So, can you check on that once and confirm?
The contact us page in your site seems to be displaying the page not found error. Also, via using this page template for the page in your site, you can add the widgets in the Contact Page Sidebar area to make the sidebar display unique widgets for the page created with the contact page template.
And lastly, if you are referring to display unique widget per pages created in your site then, can you follow this link: https://napitwptech.com/tutorial/wordpress-dashboard/display-different-widgets-per-different-pages/ for the same?