Is this the norm with adult children on holiday?

Our adult DS often joins us on holiday for at least part of the time and will often go off and do his own thing some days - absolutely fine by us. We’re not joined at the hip.
But if he’s not going to join us for a particular meal, for example, he would let us know, that’s all. He is not asking permission but It’s basic courtesy/information.
Likewise we would mention if we were going out without him.

I think its normal sadly.
It's not a case of them joining you for a family holiday as you envision in most cases. It's more the case of a halfway between a holiday of their own and one provided for them.

Was the same with 18 year old DD and her BF in Florida this year. Though slightly more understandable as my younger ones have much much different needs than the older ones. Definitely felt "in the way" though during the times we were all together its a dynamic im not in a hurry to repeat.

Ive said to DD. Family holidays she's included on until she doesn't want to do them, but actually Im not inviting her boyfriend next year, or for the foreseeable. Holidays are for us to spend quality time together, not feel like we're resented for existing on their holiday.

Is there any chance your eldest is SN too

sorry OP cross posted. I see you've had the chat. You sounded really reasonable and I hope she appreciates that. It is difficult with holidays when everyone has a different objective. At least you've broken the ice and can just carry on doing your own thing and let her do hers. I hope you still do enjoy the holiday.
The irony is she thinks your other two DC are the difficult ones... when... in fact she is just as difficult in her own way.

Yes. I agree. This would be a good first step, if you kept it very casual and two way

However, given she's already in what seems like an unnecessary strop, you should be prepared that it may not magically fix things.

In which case, you need to be practical.

Let her carry on and do her own thing.. and you do yours. Stop asking what she wants since it seems undeliverable . Make your plans with your other two DC and carry on and do your best to enjoy the rest of your holiday. Its YOUR holiday and your other DCs holiday too. She's not the main event.

In particular, I would let them make their own dinner plans.. you'd only have to pay for them and she's not enjoying it anyway.

Edited to add. If she shows any sign of wanting to change, embrace it. She's still young and you'd be setting a good example by communicating, to show her what's required. Letting her decide or not decide to comply, but getting on with your own holiday, but being welcoming if she does see the light (hope she does OPx )

She got off lightly IMO.
She was sensitive and emotional/tearful because you called her out on it by asking what was wrong.

She asked to accompany her siblings saying she would like to come with you all. She knew the difficulties in the family interactions already as she lives at home, but still expected to come along with you all.
When you agreed, she suggested her BF also come and you paid not only fully for her, fair enough, but for most of his holiday too.

At her adult stage in life, she needs to put a smile on her face and put some effort into getting along with her siblings without being moody and difficult and expecting others to put up with that drain on their holiday.

What a brat. She should be refunding you at least half.

It’s a shame she can’t suck it up when you’ve paid for her to be there. Good that you’ve had a chat, but I thing she’s been pretty ungrateful. How is fed up of her sibs when she’s only spent an hour a day with them?

Was she hoping to spend time with you all and not have to look after the other 2? But you want her to help look after the other 2 maybe? The other 2 are quite old so maybe she thought it would be a nice last family holiday with all their ages but the reality has turned out to be not what she expected.

I’m not sure where other posters have got the idea that the adult daughter was going to help look after the younger ones? People making up stuff as they go!

That being said, and playing devils advocate are you expecting her to help you? I’m presuming since the other 2 have SN that she has come last a lot of the time growing up and probably also helped looked after them as she was the oldest and you were a single mum? Its no judgement from me but maybe she wanted her boyfriend to come to make sure she could actually have a break and not be expected to act as a second parent/have to do everything her younger siblings want? She could just be wanting to spend some proper quality time with you now her siblings are older but instead it’s the same old pandering to the younger two while she gets left out?

Could have just made that all up entirely but no one else has seemed to consider her perspective at all.

I also have been on holidays with in laws and have been quite moody on a few occasions. The reason being because I spent the whole time being bossed about and told what to do which as an adult, I don’t appreciate, free holiday or not. A holiday is supposed to be a break for everyone, not just the person that has paid, especially if you have invited them. Have you asked her what she might like to do whilst you are away?

Try to quickly salvage the rest of the holiday with some confident, strong and sound advice about her poor attitude and your expecations going forward.

Instead of resentment, she needs to be feeling and showing appreciation for all your hard work in paying for them to be there with you. And unless she can switch up her current miserable mood - and take part in the family holiday fully and with cheerful positivity, she is going to be dumped not only by her BF but by you too as you are sick to death of her miserable entitlement.
She should be ashamed of herself. She is no longer a sullen teen so why is she acting like one.
Tell her to grow up, starting now this minute, and act her age or go home as you are done with her moody sulks and strops bringing the whole family down.

You've saved a whole year for this annual holiday and she is not what you or anybody else needs so she had better shape up or ship out…right out of your sight.

See if a hard talking to works OP.

I don't suppose her and her b/f have been fighting?

Where does it say she offered to help? I see her asking to join them, but not an offer to "help" with two nearly adult siblings.

But agree, she needs to speak 1-1 with her daughter to find out what's up. Could be lots of reasons.

Yes. Ask her to take the younger two out for a bit to give you a break.

I'd be careful not to fall for the BFs charms. Your DD said she wanted to help with siblings. You don't know what's going on with them behind closed doors, he could be the one causing the divide. I've seen a situation like that before where it turned out the charming and polite man was an abuser and the 'moody and distant' woman had been constantly on edge because of him.

That is great, OP! Hope it continues!

Sounds like she just wanted a feee holiday for her and her BF!! We’ve been away several times with my parents and brother and his family and we’ve always done things together, there have been odd times when various people have gone off for a lie down or bit of peace and quiet but mostly we’ve all been together to eat and on days out or sitting in the lounge together.

I would ask her about it, OP, while you’re still on holiday and she is able to change her behaviour. I would get her alone for a minute and just ask if something is the matter because you can’t understand her negative attitude and say it is affecting you and your younger children’s enjoyment of the holiday. Ask if she is really willing to help out - to be present on trips with the rest of you etc. Basically show her that you are disappointed and expected more. She may surprise you and step up - but, if she doesn’t, at least you have expressed your very justified feelings and not just accepted the situation passively. It is better for you to assert yourself and not cede control when someone is behaving badly towards you.

I'm sorry OP, what your dd1 did is not ok. We sometimes go on holiday with my adults kids (and their partners, kids) but they usually pay for themselves (although not always but would never invite themselves expecting us to pay).

If we go on a family holiday we don't live in each others pockets but we do spend most of the time together as a family. That's the whole point of it obviously because they could go on their own if they preferred not to spend time with us.
Sounds like your dd1 wanted a free holiday not a family holiday and that must be very disappointing for you.

I’m sorry OP. Sounds like they have used you to get a free holiday. Grabby and selfish.

Did she just want a holiday as your OP says that she wanted to come on holiday. Not that she'd help in any way. Has she always been selfish?

She just wanted you to pay for her holiday.

@Lomonald absolutely - your daughter is a user OP - when my son was 4 we took one of his lovely nursery nurses with us ( his favourite one) to help us out in an evening and enable us to go out - the deal was we paid for her in full to go , she babysat 5 nights and we all went out together twice and we paid - she also looked after him 2 hours every afternoon on her own apart from 1 day - she was happy as couldn’t afford a holiday - we were happy actually got a break - if she isn’t prepared to muck in and help when you have paid then I would probably just note it and not repeat

Your DD fancied a free holiday for her and her BF. Lesson for the future, only go away with adult DC on holidays they're prepared to pay for themselves. You can surprise them and help now and again if you want to, but its important to know they're invested in the experience and your company rather than just taking advantage of a freebie, which leaves you disappointed and resentful.