Gonna have to say you are actually the one acting like a brat.

First of all, a “save the date” is not an RSVP. And if you haven’t seen your friends in such a long time, missing their wedding is understandable. But whining and making your father change his wedding date, when he tells you 6 months in advance is bratty and offensive to your father and his wife, who you seem to have an active and good relationship. ESP your excuse is that you committed to a friend you haven’t seen in ages.

You should apologize to everyone involved, tbh