I think we need a bit more information on exact circumstances, but purely based on what you’ve said and on similar situations I know of (including my own) I think YABU.
Multi-generational family holidays are usually different to those a young (or early middle aged) adult would choose or could afford. For instance, my partner and I can generally only afford to go camping with our young daughter. This is not something either sets of our parents would want or be able to do. We are often invited on holidays with our various families, and while we do offer to contribute, they usually say we don’t need to - though we always try and share food costs/ split meals out etc. But they realise our circumstances and very different to theirs.
And these differences are really important to understand before you make any decisions on paying for holidays and such. For instance:
- those in early or mid-careers are probably going to be earning significantly less than those getting towards the end of theirs;
- the young and early middle aged are growing up in a time when housing costs are astronomical. Renting is incredibly expensive and buying a house is out of many people’s hopes or abilities. Even for those who’ve just about made it onto the housing ladder, mortgages are terrifying and the step up to a bigger family home can feel nearly as hard. All the while those that started their homeownership in the 80s,90s and even the early 2000s are benefiting hugely from the property price boom. Many own second homes (which isn’t helping)!; and,
- Those whose children are grown up (even if still helping a bit) now have fewer expenses, while those who are just starting out are struggling to work out how to pay for bills, and young families, and houses and such.
Absolutely, you should be able to enjoy your money now and hoping to worry less about costs of things, but you also need to understand that ‘being in work’ does not mean they are financially stable, that they can afford the same things as you, or have the same financial priorities.
Clearly one of the things your partner thinks is a way they can enjoy their money is by financing family holidays: family time and memories and enjoyment with their children. To cut that off because they now work and so should be able to pay their own way seems unfair to almost everyone involved. Unless your step children are earning lots and are relatively unburdened, then the reality is that if you refuse to allow your partner to keep helping to fund these holidays then the holidays are unlikely to continue.
Also, if this is your partner’s money then really it’s up to her.