My FI family is first generation Vietnamese and I am from the U.S. My FI and I have tried to incorporate elements of his cultural into our wedding plans, however inevitably most of the wedding has skewed towards my side since I am the bride and doing most all of the planning. This has inevitably caused some strife between the family, but mostly manageable. My recent dilemma is that I ordered and prepared my invitations. They are a pretty standard all-in-one invitation, and we pre-posted them and made it easy to fill out. My FI insisted that we hand deliver the invitations, as this is part of Vietnamese culture. I agreed, however when we delivered them, the family basically straight up told us that they aren't going to return the RSVP cards and should just assume they are coming. I find this incredibly rude, and I don't think I was able to hide my disappointment. Their response was that "invitations are for non-family" and that it's assumed all of them are coming. For context, we have a somewhat small wedding (100 people) and 35 of them are family members on my FI's side, so here I'm having a dilemma. Do I just assume all 35 of them are coming and work it into my seating arrangement, or cause more discord over insisting they return the RSVP cards, even though I know it's insulting to them?