Sabrina!
I would probably feel the same way as you at first - its def a tough situation but i think the other girls pointed out some some positives Like you get to share this fun time with your sister!!
Also to answer some of your concerns – I think it would be worse if you were both having a local wedding or both having a destination wedding but since they will be so different there will be no comparison.
It sounds like there will be a long enough time between your two weddings that for the ppl invited to both it shouldn’t be a big deal. Your friends and family love you and will be there in Jamaica for you regardless of your sister’s wedding!!!