abbyful

My fiance has 3 friends that all said "yes" months ago to being groomsmen for our destination wedding. Now that it's getting closer and we're sending them hotel info and all that jazz, they seem to be getting iffy about going because of airline cost. They knew from the start it was a destination wedding, why did they agree if they were unsure?! Anybody dealt with this? It sucks because we were gearing up to order the groomsmen's gifts and shirts and everything. I guess I'm glad we didn't order them yet! I told my fiance we can offer to pay for a night's hotel stay for each of them to ease their financial burden a little. We don't have enough money to pay for all their travel costs. And it's not like they even have to pay for tuxes, we're just doing khakis and linen shirts. They can wear khakis they already own, the shirt is the only new attire. We may even offer to pay for the shirts. Is it rude to give them a deadline, like "we need to know by April 1 if you'll be there or not"?