Aw. I read your posting, then all the threads. Everyone's so absolutely right. But I had this vision of you sitting there all crestfallen. I would definately not surprise them. Very bad idea. If you really can't contemplate going somewhere completely different (and they may well respect you more for it. You've said you're close. So no harm done. And you can discuss your different holidays afterwards at a lovely family lunch or something); then be up front. Say you've booked a holiday not too far away, as you've enjoyed the trips there so much previously, so would they like to meet up for a day. They may well have thought you'd feel like a spare part without your sister along, but if they've turned their backs on a ready made babysitter! then I feel they just want a holiday by themselves. It's not an insult or anything. Just needing a bit of space maybe. To reiterate, think the surprise is a very bad idea.