If I’m understanding this correctly something along these lines should work.
$authors = array( 1, 2, 3 ); // privileged users array
$signed_in_user = wp_get_current_user(); // get current user
// check if singed in user is in authors array
if ( in_array( $signed_in_user->ID, $authors ) ) {
$query = array(
'posts_per_page' = -1,
'author__in' = $authors
);
}
else {
// alternate query for other users
}
$posts = new WP_Query( $query );