Steffen J?rgensen

Ok, I was only looking at the frontpage — and therefor didn’t see much WP related code.

The style.css file says:

/*
Theme Name: About.NetSol
Theme URI: https://networksolutions.com
Description: CSS for About.NetworkSolutions.com
Version: 3.0
Author: Network Solutions
Author URI: https://networksolutions.com
*/

However, I don’t think it’s a WordPress site…

Just download the wp-config.php to your desktop and edit it with Notepad or something.

Can I somehow change the page ID′s?

No

You can use the category-{slug}.php

https://codex.www.ads-software.com/Category_Templates

You use IDs to include/exclude pages from the menu:

https://codex.www.ads-software.com/Function_Reference/wp_list_pages#Exclude_Pages_from_List

Only by making the website one big image or Flash-file, you can prevent such thing.

Use a different pagetemplate for that page.
Or, use conditional tags, like so:

<?php if ( !is_page('page-slug') ) {?>
<?php the_title(); ?>
<?php } ?>

I don’t see a problem.
Blog posts essentially are nothing but articles…

A link to the site would help a great deal…

Just use the YouTube “<embed>” code.
It is shown on every YouTube page when you click the “<embed>“-button just below the video.

https://jobs.wordpress.net/

A link to your blog/website would help a great deal.

the “large” and “larger” sets the font-size relatively to the font-size defined by CSS:
https://www.w3schools.com/css/pr_font_font-size.asp

If you have a paragraph with a font-size of 12px and you have a span inside that like:

<p>this <span style="font-size:larger">is sample</span> text...</p>

the text inside the span will (logically) be “larger” than the text outside the span.

I’m not sure if there are specific sizes or that depends on the browser rendering the text.

I usually do it like this:

HTML:
<p>this <span class="larger">is sample</span> text...</p>
CSS:
p{font-size:1em;}
p.larger{font-size:1.2em;}

I cannot put in any themes to the users that I created

What do you mean by this?