The problem is that you use inline HTML code to style your article content.
Inline HTML overwrites the CSS settings, which means your font size is controled by your HTML code added as articles and not by the template.
Thats why you have different sfonts all over your page.
The solution is simple: don´t use inline HTML.
If you copy and past text from another website you also copy and paste the inline HTML code into your joomla article. Thats the most common reason for that behavior. And it could be that you even don´t know that you also add style informations directly into your article/module content. But also if you convert Word docs into HTML you will have the same problem.
To remove it open your article content in your Joomla backend and open the code window (hit the small "html" icon) and past your text here. Than you will just transfere the text, not the included code.