Hugs!
First off, you are NOT a spoiled brat. You are reacting to the situation the way any normal person would!!!!!
You have a wedding planned, you have paid to hold your wedding spot, to vacation there, and you have family who has also invested time and money to be there --- you should be pissed and upset and angry.....
Thankfully your family in Jamaica is able to run around and sort out some details for you. Hopefully that will put your mind at ease some.
Have you tried to contact the resort? The airline? (I don't know how your packages work from Ireland - do you book everything separately?) I would certainly be seeking out some recourse!
Your day will still be beautiful and magical and special no matter where it is held. I know that is hard to see now, but you will be with your fiance, your friends, and your family. Your marriage will be beautiful. Hang in there... please keep us posted.