I think you will find a lot of support and advice on this topic here. This is a very common and painful situation which I think many destination brides have to deal with (who would have thought a wedding in paradise would not sound appealing to the families?!?!?)
I had to deal with this from my side of the family for months before the wedding. Even with a very solid reason for why our wedding had to be on the island, I was constantly questioned about it and complained to. My FI and I both really wanted a beach wedding and since his family is from South America, the Caribbean was perfect!!! My Mom and 2 aunts would NOT leave it alone and constantly questioned me whether people would travel so far and how hot it was gonna be and how this and how that. They told me that nobody will come. They told me that it is rude and inconsiderate to expect people to spend so much money. And etc etc. And all of them go on vacation to the Caribbean at least once a year!!!! I cried over it many times and went back and forth for a couple of weeks, even looked at local places which I could NOT get excited about (a wedding in the U.S. would also mean not much family from my FI's side would be able to attend since it's so far away and so expensive, plus visa hassles). Finally my now husband put me out of my misery and just said that we are going to do what will make us happy and if someone cannot come, so be it. It's not like our families could NOT come, they were just complaining and since they have never been to a destination wedding before, had no idea why we were doing something so unorthodox.
Fastforward to the wedding, everyone had a good time. Yes, it was hot (which I like). Yes, it was pricey. One of my aunts totally ate her words and keeps talking about how we need to do a reunion for our anniversary since she had so much fun.
The bottom line is that if your family CANNOT travel then you might want to reconsider. But if they are just giving you a hard time and do not understand but they CAN come, then do what you guys want to. It's your wedding after all. And there will always be someone who will complain.