First fix needs to be to distinguish between paragraphs that are indented and those that are not. Your sample shows that all paragraphs use the class="algemeen" so currently no way to distinguish between the two. I think they tried to do that with the algemein + algemein css code, but obviously not working for you. Actually I don't know if that is a valid method as I have never come across it.
As for the extra line spacing, obviously it is not in the algemeen css, so then it may be a level higher. Are there and <div> or <section> tags that capture all the paragraphs? Maybe the <body> tag contains the extra line spacing. Check the css code for these tags.
Also, you don't need the language on every paragraph. Yep, I am aware you didn't code the book, just commenting. Same with the heading- should really use the <h> tags.