Sample Set Up with Multiple Relationships

p2p_setup.php

<?php 
// Don't copy the php tag above.
function sfws_books_to_relationship() {
    p2p_register_connection_type( array(
        'name' => 'bookes_to_authors', //Give it a name that you can reference
        'from' => 'books', // This can be the slug name of your CPT as well
        'to' => 'authors' // This can be the slug name of your CPT as well
    ) );
    
    p2p_register_connection_type( array(
        'name' => 'bookes_to_illustrators', //Give it a name that you can reference
        'from' => 'books', // This can be the slug name of your CPT as well
        'to' => 'illustrators' // This can be the slug name of your CPT as well
    ) );
    
    p2p_register_connection_type( array(
        'name' => 'bookes_to_publishers', //Give it a name that you can reference
        'from' => 'books', // This can be the slug name of your CPT as well
        'to' => 'publishers' // This can be the slug name of your CPT as well
    ) );
}
add_action( 'p2p_init', 'sfws_books_to_relationship' );