Twaddle. People make decision and plans together. Once communication goes down, the relationship goes tits up.
We don't know anything other than the OPS 'side' of the story. Then the pitchforks and guillotines come out.
No-one knows, for example, the financing of the original holiday. If I had perhaps been saving for some years, or perhaps received an inheritance I don't think I'd be too happy at being told I was taking an extra person. After normal conversation, it would probably be the consensus that the daughter would come too. But I would not be told how to spend my income nor my time.
Also, second wives, often have issue at the level of child support given to first families. (to put that in perspective, my female friend is shelling out over half of her salary to her ex-husband because her 15 and 17yo son decided to move in with him - no ground rules, girls allowed to sleep over, limitless pocket money - absolutely nothing to so with bad parenting on her behalf BUT her ex-husband expects her to pay and additional sum when expensive school trips are arranged and for her to additionally contribute to their holiday wardrobe)
HOWEVER, read between the lines of the OP - he's blaming the new wife (All agreed? Spineless) but who did the initial stirring? The other children. Why? Perhaps, just perhaps, the dynamics of this 'blended family' (never heard that phrase before) aren't condusive to 2 weeks in Mickey-Mouse-Land -and everyone will feel like having a holiday to get away from each other at the end of it.
Always two sides to every story