They are putting themselves between you and your family. Family is family no matter what. I would try to not think about it and enjoy your trip. They knew ahead of time and went ahead and planned the wedding. You say you are no longer in the wedding because of this so there is tension already and as you state they are getting hostile and combative, no way would I go, Acting like children--A good friend would try to understand, she might be very disappointed; but, would accept. What kind of friend acts like this. They are not only trying to change the trip; but, use your money for travel expenses. I disagree that this is more important than a family trip--you can do something afterwards; but, she will probably be mad, but she can get over it or not. I am older (just telling you what I would do under the circumstances) and don't have anyone but my brother left in my family and for me it would be a no brainer---no thought, no discussion just the trip---- don't even ask and trying to say this nicely--stop with the worrying about them, they didn't for you, stop the guilt trip, you are being too nice. Go shopping and buy something to wear for the trip. Focus on what is really important.