While the perspective of the non resident children, is that stepsiblings get all the time or more time with their dad, that may not be a positive experience for the stepchildren in reality.
If a father isn't bothered about the time he spends with his own children, how great a dad can he really be to stepchildren?
Ex wives often think he's playing happy families with the stepchildren, but that's not always the reality.
A crap dad, will be an even worse SD... because he can get away with doing even less, as they aren't his kids.
I'm sure there are some men who are good dads and good stepdads, but this notion of him playing happy families really isn't true in many cases.
Those adult SC whose dad went on holiday with his stepchildren...should lay the blame squarely where it should be placed and that's on the head of their fathers, who chose to spend minimal time with them. Kids often don't see the faults in their parents as young children, but hail him as some kind of superdad. Superdad wouldn't ignore you and jet off every year without giving you a second thought.
It's so much easier to blame the SM, because the reality isn't great.
I can be objective about this. I'm neither a stepchild or stepparent, but I do work with blended family members and hear lots of their issues.
My DNs are also stepchildren.
My SIL is their SM and I do watch the interactions fairly closely.
In the OPs case, there is nothing wrong with going away if the SC are going away next year. There's no reason your DC should miss out.
The only problem is if she's flaky and suddenly the holiday isn't happening and yours is already booked. Then you're a bit stuck.