My FILs are well off and very generous towards us. They let us use their professional sports team season tickets, pick up every check when we go out, and are contributing a lot to our wedding. We just got back from an all expense paid trip to a Caribbean island which his parents paid for and wouldn't hear of us spending a dime. I feel awkward because we are so broke right now paying for our wedding and waiting for FIs commission checks to come in that I could not have picked up a check on this trip if I wanted to and even though I said thank you at the end, I feel like it's not enough. What can I do to let them know I really appreciate their generosity?
Also I never once heard FI or his sister thank his parents once on this trip (or in general). My family is not super well off, so I have no way of knowing if this is normal or not. And now that I am becoming a part of their family, is it weird that I am thanking them so much? It all just feels awkward to me. I want to do the right thing, but not make people feel weird.