As the OP pointed out, they will not be attending the original wedding in the Caribbean, the OP says the ceremony will be in the US, the second ceremony is a repeat . I think the first ceremony is more special then many people believe, feel free to disagree. I think the sister may regret not doing more for the original, I wonder how often that happens.
Knowing that the second ceremony is a recreation, does that change your opinion? If the OP attended the actual ceremony in the US, are they required to attend the after party in the Caribbean or is this getting excessive? How many ceremonies for a couple do you typically attend, am I out of touch thinking one is enough?
What? Where did the OP say they were having more than one ceremony? But, regardless, I've witnessed pre-wedding courthouse ceremonies and attended just post elopement receptions and felt just moved in either situation.
Post #1, the OP said there would be a ceremony in the states, then followed by saying there would be a ceremony in the Caribbean. I don't know why, perhaps there are travel restrictions due to a VISA requirement (the OP stated the fiancée was an immigrant, I have no way of knowing their status, lets assume the OP is knowlegeable and I am not). By the original posting, I counted 2 ceremonies were being held, why would anyone assume the OP is wrong?
“Since they must get married in the US for the license to be valid”
“they have decided to have a destination wedding somewhere in the Carribean”
I agree, I get moved every time I witness a wedding, inviting more people is usually the best course of action. I discourage anyone from having a closed courthouse ceremony, around here its $75 and the marriage commissioner will stop at your house, park, or other location. For $25 you get my witness service, I provide a required service and dress up nice, but would you rather have random stranger or a family member at your wedding? Ultimately it’s the couples choice, I’m only there to provide a service. I don’t say anything, I’m just a background person who signs the form, no one ever recalls I’m there.
As you point out, when you've been a witness at a courthouse its a very special event. I sincerely hope the OP attends the ceremony in the states. I assume you also recommend attending the original, they can be lovely no matter where they happen, I feel we agree on this.