AIBU to not pay for them?

She is, she just doesn’t want to pay, and why should she? It’s an expense she didn’t expect or offer

I don't think you're necessarily being U. I think it's impossible to say really, without knowing the dynamics of your wider family. In some families, that would be just be a case of the dad saying - looking forward to Sat, we obviously dont expect you to pay for the others on top, so I'll cover them. In other families it would be a huge drama. Just depends on the protagonists here. It also doesn't need to be done right there and then at the table! No need for any of the kids to be aware of the finances of the occasion!

So? They didn’t need to be included. OP’s SIL doesn’t seem to have any expectation that she would treat his children like her grandchildren, given that they’re not.

They’re not OP’s family any more than her daughter’s mother in law is her family.

I grew up in a blended family, no living grandparents of my own but my SS had a living grandparent. He made me and my siblings very welcome, brought us cards for birthdays and other occasions and often gifted us money which he didn't have to do at all but he also looked at our children as his own great grandchildren and enjoyed all our company. He paid for a fair few family meals out and there was no ' your real family I'll pay for you, your not so you pay' sort of deal. He did it in the early days before we got to know him properly . I appreciate it may add extra expense OP but these are your granddaughters half siblings and I'm sure she would like for them to be there to celebrate with you all? If it's possible I would pay for the extra kids, although an offer from your DD or SIL would be appreciated. Hope you manage to resolve this without any family rifts occurring

I don’t think OP is planning to start an argument. And if they feel excluded it’s because their dad and SM are piss takers

And I don’t agree that feeling part of the family requires money. OP has said they’re welcome to come to the meal. Isn’t that enough?

But the SIL wouldn’t be going out with his ex in-laws so it’s not remotely the same . That’s a bit like saying would the SIL and daughter send their joint child to stay with his ex partner for the weekend , it’s hardly likely is it .

So it’s cheeky fuckery to massively add to someone’s else’s expenses, when you haven’t asked or had approval? Ask long as they’re family? Why can’t OP’s son in law pay for them?

It’s not disgraceful at all. Why should the OP be begging to be involved with kids who aren’t related and she barely sees? And I imagine the meal is on her GD’s birthday and son in law is the NRP rather than purposefully done to exclude them.

Can you afford it?

If so, you are just being mean.

This is sad. Read the other threads about step grandchildren being excluded by grandparents. Make those kids feel welcome.

I wonder if the son in laws ex partner's parents will invite the OP's granddaughter to their family events? I expect not.

I often see in blended families that is the new step grandparents who are expected to treat all the children the same but those expectations are not put on the step childrens grandparents to include any new half siblings.

But they are your daughter's family? How unkind of you. Maybe actions like this are why you don't know them?

It would feel pretty transactional for the stepkids if everyone was arguing about which schmuck actually had to pay for them. To feel part of a family you have to be...treated the same as everyone else. Shocker!

I don't think it's "begrudging" the SGC at all! OP has said she's not exactly rich and she doesn't really have a relationship with them.
It doesn't mean she doesn't like them, just that she hasn't seen them very much. And in that case, I don't see why she should be having to pay for them! That would be awkward for me, like paying for strangers!
I also think it's a bit cheeky if the parents assume that they'll coming to the meal now and be paid for.
I'd mention to your DD that you hadn't really budgeted for 2 extra and see what they say.
Hopefully they'll understand and arrange for another time or offer to chip in x

So to feel part of a family you have to have money spent on you? How transactional

Why shouldn’t the DD and SIL pay?

Yes re the cost - I once had family visiting and took them out for a meal (father and son). The son who was 10 at the time ordered a fucking sirloin stake! I paid £29 for him to eat a sliver of stake 3 chips and to say “I don’t like it” while his dad said fuck all (it was the first and last time I accosted a visit). He also ordered 4 cokes. Kids don’t always realise the cost of things and adults don’t always check them on it

It did but perhaps not for everyone.

And I’m sorry this was the story of your life.

But OP doesn’t know them and never sees them. Should she have lied?

Lie? No.

Make them more welcome and make more of an effort with them from the start? Yes.

As I’ve said who they are isn’t relevant - it’s cheeky AF to invite people along and expect someone else to pay

Of course it’s relevant. They’re family. And it’s disgraceful the birthday celebration was organised in the first place on a day the children were with their mum. They’ve been excluded from the get go.

The OP has NEVER said she doesn’t want the kids there this is just about money.

So half of these posts are answering a problem the OP doesn’t have

I don’t need to imagine it…that was my life 😂

Obviously the sarcasm didn’t come across.

Do children need the validation of some woman they barely know before they consider their siblings as family?

While it may be an unpopular opinion, I'd contact whoever in the family you made the arrangement with, and tell them that due to circumstances outside of your control, you're going to reschedule the meal out.

As someone who grew up in a blended family I maybe clapped eyes on my step siblings Grandparents maybe three times. I never thought to make a fuss of whether I was part of their family because I wasn’t and that was ok. In fact I hated feeling patronised about being part of a blended family. I still had 2 parents so didn’t need extra random people who didn’t choose me to be in their lives.

Why do people behave like SC have something missing from their lives?

Children are odd as they tend to consider their siblings as family. They even want their siblings to be there at their birthday celebrations.

(They can be very different to bitter munsnetters.)

But OP doesn’t know them and never sees them. Should she have lied?

As I’ve said who they are isn’t relevant - it’s cheeky AF to invite people along and expect someone else to pay

Speak to your daughter, tell her you had planned to pay for dinner as a treat but had budgeted for 6 not 4. Dont do it at the restaurant. I'm assuming they are grown up and wouldn't be having kids meals?