order the meta query results by 2 custom fields

You forgot to use relation in meta_query .
I think this will work:

$args = array(  
    'post_type' => 'brewery',
    'post_status' => 'publish',
    'posts_per_page' => -1, 
    'meta_query'     => array(
    'relation' => 'AND',
        'review_rating_meta' => array(
            'key' => 'review_rating',
        ),
        'reveiw_count_meta' => array(
            'key' => 'reveiw_count',
        ),
    ),

    'orderby'    => array(
        'review_rating_meta' => 'DESC',
        'reveiw_count_meta' => 'DESC',
    )
);