This is mostly theoretical, but I would like e-hell's perspective on it nonetheless.
In the not-too-distant future I would like to take my parents on a trip to the US. This would be an expensive trip that would require a lot of planning and saving, but I would like to bear the cost entirely as a gift to my parents. Both have wanted to visit the US for a number of years, and my father has a relative there that he would be delighted to visit.
I have one sibling, Trent. While it would be nice for him to come along, to make a family trip, I have to admit that I am not really willing to add to my expenses and pay for his trip as well. It should be noted that neither of us have families or partners that need to be considered. This situation may change in the future but for now, he would be the only other person to enter the equation.
If I do go ahead with this holiday, can I say to Trent: "Hey, I'm paying for Mum and Dad, if you'd like to come along here are airline prices, and accommodation fees"? I know that with most things it would be more practical to book as a four, so if he accepts should I say: "This costs $$, your share is $"?
Incidentally, has anyone done a big family holiday as an adult with their siblings? How did you handle costs, planning, etc?