How can I query posts from multiple roles?

Question

Just do the get_users() twice and merge the results:

<?php
$friends = get_users( array( 'role' => 'friends' ) );
$enemies = get_users( array( 'role' => 'enemies' ) );

$friends_n_foe = array_merge($friends, $enemies);

$IDs = array();

foreach( $friends_n_foe as $person ) {
    $IDs[] = $person->ID;
}

$news = new WP_Query( array( 'author' => implode( ',', $IDs ), 'post_type' => 'news', 'paged' => get_query_var('paged') ) );
?>