SOLVED!
I found this post, https://itch.io/t/442426/website-layout-forced-mobile-layout by https://itch.io/profile/harley-torrisi
He suggested placing this code into the CSS:
.right_col.column {
visibility: hidden;
height: 0px;
}
After getting CSS access from an Admin it was as simple as pasting that code into the Custom CSS field in the Theme Editor.
Poof, no more screenshots on mobile devices.
Also, regarding the page-width problem. I finally tracked that down to the Admin Dashboard shown at the top of our own games. If I view my game page while logged out, I get the standard Itch header and everything lines up properly.
I hope this helps someone else who may have struggled with these problems.
-John