I agree with TotemPole99. Tell them there will other trips later on.
If they really are your friends, then they'll understand. If they don't, then they're not.

I finally broke down this past Christmas and told my mom & siblings that we (my wife & kids) would not be seeing them during the holiday season (first time in 30 years). It's a long story that I won't get into here but I can say it was the most stress free Christmas I've ever had.

Just my $0.02.