Cannot retieve the_content() and the_author() – both returning empty strings

get_the_content and the_author have to be in a loop so you would need to use other functions to get the content you need

global $wp_query;
$post = $wp_query->post;
$page_id = $post->ID; // page ID
$page_object = get_page( $page_id ); // page stuff
$author_id = $post->post_author; // author ID

$page_content = $page_object->post_content;
$author_name = get_the_author_meta( 'display_name', $author_id);