Would you expect your spouse to say something?

do they have contact with their own other parent

I also don’t think this makes any difference. Not having a relationship with their parent doesn’t mean there’s automatically more responsibility on their step-relatives to step up and plug the gap, unless they want to.

This seems to be out of line with most people on MN, going by other threads though.

You said A’s parents don’t have much relationship with the stepchildren, so no, why should they pay?

So B thinks A’s parents should pay for their DC too?

I disagree.

And it doesn’t make any difference if it’s Disneyland.

Does B think its a problem because they feel that their DC's are being excluded? If they have no relationship have they been excluded in other things, are they included in Birthdays and Christmas?

What does B want A to say to their parents?

It's all going g to to depend massive on tbe detail. How old are the older kids, do they have contact with their own other parent, why is there little relationship between the older kids and grandparents? How long has A & B been together and acting as a family And so on.

In some situations I would say its not OK. In some I would say it is OK.

The grandparents are well within their rights to only pay for their blood grandchildren. You say they don't have a relationship with the dscs. It's their money to do with as they please and are being very generous anyway.

I'd take it as the cost of a family holiday is being hugely subsidised, meaning the parents can afford to include the dscs and everyone can go and have a lovely time, without money worries.

My one proviso is that if the parents can't afford to include the dscs, then that should be explained to the grandparents and the offer should be politely declined.

How long have A and B been married? If a short one, then that’s reasonable, especially as parents don’t really know teens.

I guess parents are not excluding step-children. As they’re still invited, but perhaps don’t feel they have enough money to cover all children.

If they’re the kind of grandparents who will buy all children - step and job-step icecreams on holiday, then I would proceed. If they will only buy bio- children, and not step, then that’s a problem.

I think it's fine for A's parents to pay for their grandchildren to go away and that A&B fund the step-children. It still makes the holiday considerably cheaper than it would have been!

I can see why B would be a bit hurt but at the end of the day the step children are invited and it's still saving you both so much money.

How long have A and B been together? How old were the stepkids when they got together? Why hasn't the lack of relationship with A's parents been dealt with sooner?
Basically if the lack of relationship has been going on for years it's probably too late to do anything about it, but if I was going to tackle it it wouldn't be as a money issue first I'd try and improve the relationship before expecting money/holiday.