Enrolment

I would create an events and observer file in your theme:

db/events.php

$observers = array(
    array(
        'eventname' => '\core\event\user_enrolment_created',
        'callback'  => 'theme_????_observer::userenroled',
        'internal'  => false,
        'priority'  => 0,
    ),
);

classes/observer.php

class theme_???_observer {
    public static function userenroled(\core\event\user_enrolment_created $enrolment) {
        if (!empty($enrolment)) {
            if ($enrolment->courseid != 10) {
                enrol_try_internal_enrol($courseid1, $enrolment->relateduserid);
                enrol_try_internal_enrol($courseid2, $enrolment->relateduserid);
                ...
            }
        }
    }
}