Hey There,
I really feel for you and know exactly what you are going through, because I went through the same thing. My dad's family was making a HUGE deal about us going away. My aunt told me I was being selfish in that im basically asking for a $6000 wedding gift (for all her family to go it would cost that much) that im basically choosing to elope by going away blah blah blah. She also said that people cant afford this, I have everything handed to me and wouldnt know what its like to have to pay for a trip (which is complete bull sh*t) and was soooo insulting. She said so much more crap but Im not gonna go on about it. So all of my dads family complained about this and My mom or I dont even talk to my aunt any more. She was so rude that I'm no longer even sending her an invitation. We did NOT change our plans because of his family making a big deal about it. You and your FI need to do what you want. Its your day and you need to be happy.