AIBU to not pay for them?

Why would they despise her granddaughter? They have their own grandparents

She’s hardly treating them like ‘shit on her shoe’.

Sure she gets a say on what she spends her money on. She will also need to bear the consequences.

Nah your daughters husband has orchestrated this on purpose and invited his children.

OP says it was due to their Mum's plans changing. That would be quite the orchestration.

I think rearranging would also be churlish actually

let’s hope that Op doesn’t get old and require any support from her son in law - because he’ll remember how she thought of his kids. And probably quite rightly say it isn’t his responsibility.

Yes, extra people. Their relationship to him and their granddaughter does not oblige OP to pay for them.

‘For his MIL to pay for’ - presumably she gets a say about what she spends her money on? IMO he should be the one paying, not OP.

So you were expecting to pay for 4 meals & now it's 6(?) for example?

I think if you cancel/rearrange however you phrase it it looks as if you don't want the SC there.

Can you pay for yourself & the kids?

Can't you explain to your daughter that it's now too many for you to pay for everyone?

Wht would you ever exclude a child

Extra people? It’s not like DH invited a couple of colleagues for his mil to pay for. They’re his fucking kids!!!!! The half siblings of OP’s granddaughter.

How will you feel if your daughter’s stepchildren end up despising your granddaughter? Because they will if they are continually treated as inconvenient baggage, whilst your granddaughter is the golden princess.

why don’t you reframe it: when you’re dead, your dd and her DH are dead, wouldn’t you be happier if your grandchild has her half siblings in her corner?

I don’t know if you are naive or simply mean, but you cannot treat people like shit on your shoe and expect no consequences. You should welcome them and pay for them. And remember they are children, children whose parents broke up. And hope that they have a fantastic relationship with your granddaughter.

It’s bold to invite extra people and expect you to pay.

YANBU to rearrange or to make it clear that he’s responsible for paying for his children.

I wouldnt ask them to pay for step kids. I think it's a bit crass. However it's reasonable to cancel the meal now that it's a more expensive than originally planned, I'd say let's change it to pizzas and cake at home or you dd and do something another day the three of you.

It's just the once. On your GD s birthday. Make it a special one for her. Pay up without creating a bad atmosphere. How much are we actually talking about here? Another 70/80£? Definitely not worth causing any ill feeling over.

Nah your daughters husband has orchestrated this on purpose and invited his children.

You'd already explained who you were paying for, it isn't fair of them to expect you to pull an extra 50% out of your ass ??

I'd apologise and rearrange and state you've budgeted a specific amount due to the costs and hadn't expected them to be joining. Whilst they're welcome and part of the family you haven't allocated enough to pay for them as they were added short notice.

I'd rearrange.

If we agree to pay for a meal sil always suddenly adds about 4 more guests, it’s really annoying. it’s nothing to do with my relationship with the guests (or yours to sgc) and everything to do with agreeing to pay for something based on the budget, then that budget suddenly shifting. It’s really rude.

equally however I’ve been the step child that everyone makes it very clear is an added burden and cost and they’d rather you weren’t there. If they don’t have form for being cf and you can afford it I’d maybe let it go for their sake.
if you decide to say something I do think it’d be unpleasant to say it’s because of your limited relationship with them, it makes the gift to your dd seem very transactional as well.

I actually think that's totally reasonable 🤷🏻‍♀️

You don't get to just bring along two extra mouths to a paid for meal and expect them to be covered too! Especially as they're not really "family" - they're the husband's older kids, who the OP doesn't have a grandma / grandchild relationship with.

I'd quietly speak to your DD and say that's out of the budget, you're happy to go ahead as planned if they can cover the extra attendees or reschedule if they can't.

Going against the grain but I think DD and SIL have got a bit of a cheek bringing extra guests without asking you, at the very least they should have said “Of course we’ll cover the extra cost”

I cannot imagine my granddaughters step grandma doing this . It is so important that a step child is accepted and included at all times.

Offer to pay for all the kids. Don’t isolate the step kids.

There are so many really odd threads today.

I don't think it would be OK to specifically say that you'll pay for everyone except the step grandchildren.

However, if money genuinely is tight (as opposed to you just not wanting to pay for them) then have a chat with your DD and point out that you can't stretch to paying for 6? people instead of 4, so can you split the bill in some way? Either you pay for all the children and yourself and DD and DSIL pay for themselves, or maybe a straight 50/50 split down the middle.

Whatever you do, it shouldn't come across as "I don't want to pay for step GC" as that will come across as mean spirited.

Do you want to build a relationship with them?

If not have a quiet word with your daughter and reschedule. It’s rude to invite new people to a meal someone else’s paying for without discussion.

I like the suggestion of offering to pay for all the DC and not the mum and dad.

Depending on age that could be near enough an extra 50% on your bill. I think I'd try and find somewhere cheaper to eat so your original budget will stretch to pay for everyone, maybe somewhere with a kids eat free offer or a fixed price brunch? Treating them the same could be the start of forming some lovely family bonds.

I wouldn’t begrudge my step-grandchildren (because that’s what they are) a meal for their sibling’s birthday, how mean.