$authors = get_users( array(
'fields' => 'ID',
'role' => 'your_role'
));
$my_query = new WP_Query( array(
'post_type' => 'your_post_type',
'author' => implode( ',', $authors )
));
$authors = get_users( array(
'fields' => 'ID',
'role' => 'your_role'
));
$my_query = new WP_Query( array(
'post_type' => 'your_post_type',
'author' => implode( ',', $authors )
));