Some WP problems


First problem:
I’ve installed the plugin Yoast SEO and activated the breadcrumbs. Now sometimes this breadcrumb isn’t correct, when you click on a permalink of a post, the breadcrumb “forgets” the category.

It should say: Home » Nieuws » Isoleer je dak het eerst

Second problem:
I’d like to alter the layout of the comments.php, but when i open this file, it looks like a completely different (English) file than the one that is being displayed on the link above (it’s in Dutch???). How can I find out which .php file my website is using for the comments form?

Third problem:
My navigation: If you hover over the navigation, the background becomes white. When you hover over the subnavigation, the main nav white background disappears. Any solution for this? I’m using a custom menu…

Fourth problem:
I’ve hardcoded Nivo slider into my layout on the homepage, but it won’t work like I want it. Nivo slider needs to resize the image to the height and width I want: width:450px and height:340px.
Now I notice the slider resizes the height, but not the width. It stays 600px wide.

This is my code:

<div id="slider">


				$tmp = $wp_query;
				$wp_query = new WP_Query('posts_per_page=10&category_name=referenties');

				if(have_posts()) : while(have_posts()) : the_post(); ?>

            		<a href="<?php the_permalink(); ?>" title="<?php the_title(); ?>"><?php the_post_thumbnail('featured-thumbnail'); ?></a>

				<?php endwhile;

				endif; ?>

			</div><!-- close #slider -->
// Featured image
	if ( function_exists( 'add_theme_support' ) ) {
  	add_theme_support( 'post-thumbnails' );
	add_image_size( 'featured-thumbnail', 450, 340, true );

This PHP code should resize the canvas of my slider, but it doesn’t…

No one who has a clue?