What do you advise me to do to inform my family about my marriage to a young man they repeatedly rejected, knowing that my marriage took place without their knowledge, and that their rejection was not for legitimate Sharia reasons?

The guardian is a condition for the validity of marriage according to the majority of jurists. However, if a judge who holds the view that marriage without a guardian is permissible rules on it, then it is valid and cannot be annulled. Therefore, if your marriage to the young man was officiated by a Sharia judge, it is valid. You should gently inform your family and seek the help of someone who holds a respected position with them, bearing in mind that a guardian should not reject a suitable suitor.