1. Try to use child theme from attachment

2. Sorry, not quite sure what do you mean. Can you pls provide more details with screenshots?

3. I suppose problem will be resolved after zoom magnifier using.

Child theme

2. You need to add next code to functions.php file in child theme.

function thegem_child_init() {
    remove_action('thegem_woocommerce_single_product_right', 'woocommerce_template_single_excerpt', 35);
    remove_action('thegem_woocommerce_single_product_right', 'woocommerce_template_single_add_to_cart', 45);
}
add_action('init', 'thegem_child_init');
add_action('thegem_woocommerce_single_product_right', 'woocommerce_template_single_add_to_cart', 35);
add_action('thegem_woocommerce_single_product_right', 'woocommerce_template_single_excerpt', 45);

3. Picture may change only when you select variation. It is default woocommerce interface.

You need to change template woocommerce/content-related-product.php.  Copy this tapmlate to child theme directory (path must be saved). Then add next string:

$woocommerce_loop['columns'] = 3;

after this code:

// Store column count for displaying the grid 
if ( empty( $woocommerce_loop['columns'] ) ) { 
    $woocommerce_loop['columns'] = apply_filters('loop_shop_columns', 4); 
}