To never invite them again.

They were rude, you called them out on it and they won’t be invited again on holiday.

Your DF threatening to take him out of the will is immature and manipulative and frankly I’d be very angry at the threat. Your DS clearly has a good relationship with them and that’s why he’s in the will and was invited on holiday to start with. If your DF is this upset and wants to put the money in a trust with guidelines around it then that’s fine but threatening to cut him out is so foolish and would be very hurtful.

Sounds like a lot of immature behaviour all around.

Is this out of character for your ds to be rude to your parents? Has he ever done it before and what was the outcome? I suppose it's complicated by his gf being involved.
I remember my ds being a real brat to my parents once, when he was about 7 or so and they'd taken both kids for a lovely day out. I was furious with him and made him write a (sincere) letter of apology to them. My mum wrote back a lovely letter to him thanking him and saying she understood and what a lovely boy he usually was etc... I found the letter recently (DS is now nearly 30 and my parents have passed away) and it made me shed a tear.
Reader, DS remained in the will!

I think you've done everything you can do OP. I've twice taken DC's friend abroad on holiday and both times went well. Lucky I guess.

But yeah, well done for calling them out as and when you did. I can imagine it was tough.

“DS is angry at being called out for his behaviour ”

Why? He must surely know that the way he spoke to his grandparents was utterly unacceptable. I feel for your DPs who were trying to do something nice for you and your DS - I doubt they could have cared less whether the GF came or not, and only paid for her to please your DS. I can completely understand that your DPs are more than a little upset to have had their generosity abused by your DS and GF - your DS needs to apologise to them, even if the GF won’t. It’s quite possible this relationship won’t last, even if your DS has gone running off to see her - but he needs to make his peace with his grandparents, and he needs to understand that his behaviour was that of an entitled brat rather than a grandson who had been kindly taken on holiday by his grandparents as a treat. There’s no need for you to be getting it in the neck from both parents and DS - I’d be making it v plain to my DPs how disappointed I was with DS and GF’s behaviour because of the way they behaved, and that that’s the last free holiday he’ll be having. (I know he’s your DS and you don’t want to fall out with him irrevocably, but I’d make it very plain how disappointed you are and I’d be thinking long and hard about whether in future I’d so much as take him and his GF out for a burger.)

This.

Some of the things you mention about the GF make me wonder if she’s overbearing on your DS.

I would absolutely support your df in changing the will. He’s too immature to make any good decisions. And only time will tell if he is capable of that. In the mean while he doesn’t deserve anything. I would just make it very clear that she isn’t welcome anymore and she really needs to prove she’s changed before you accept her again.

Their behaviour was awful and it’s shocking how ungrateful some people can be. Your parents tried to do something nice and were taken for granted and massively disrespected.

One thing I’ve noticed in life is some people act very entitled and don’t value something when they get it for free as opposed to having to pay for it themselves. When they pay for it they tend to take it more seriously and make the most of it.

Tell them you expect your dps to be reimbursed for their share of the holiday

I don’t think this is a great idea, it’s very unrealistic and nothing will come out of it. I mean sure Op can ask if she wants but I very much doubt they’ll pay a penny given they can’t even say thanks (which is shameful) All it will do is sour things further and what’s more they’re under no obligation to pay because tbf went on the understanding that it was free.

The parents are just going to have to suck it up and know not to pay for him/his friends again and indeed think twice about inviting them anywhere even if he pays . And OP needs to sit down and have a very serious talk with her son and he should apologise to his GPs.

Hopefully, he’ll follow through on that.

Your ds doesn’t deserve it on his own behalf, never mind any concerns about any of it finding it’s way to her.

I'd have sent them/her home. Cheeky fucker!

He had balls enough to be rude in the first place, though?
He sounds completely spineless, tbh.
Not much to be proud of there.

I would have done this the second day of the holiday.

Why didn’t you, OP?

I empathise with the pp saying the6 wouldn’t let her in the house again, but that’s possibly going to make the OP’s ds resent her and dog his heels in about his gf. It could lead to him going nc. I say tread carefully whilst obviously telling them both that their behaviour was terrible.

The behaviours from both GF and your son in different ways were appalling. The GF more so I might add. How a person could be so ungrateful astounds me. I have sympathy with your parents, how utterly disappointed they must be feeling. Abused is a word commonly used nowadays but I do feel their kindness has been used and abused. They are owed a heartfelt apology from both your son and his badly behaved GF, I doubt, however, one will be forthcoming.

@PatrickDog what a coward he is.
I certainly wouldn't be letting her back in my house until they had both apologised to your parents, and you.

Well that's her no longer welcome in your home imo. She has no respect for your family.

And what are you saying to your son when he's whingeing about being called out for his dreadful behaviour? Hopefully you're reiterating that he's behaved like a rude, entitled brat.

I'm sorry OP but the girlfriend sounds very manipulative and your DS is too kind to stand up to her (that's a compliment to you, really, as you have obviously brought him up this way). There is nothing you can do I suppose unless you want to actively try to break them up. The best you can do is explain to him how manipulation works in a relationship and hope he takes the hint. Oh, and do nothing to support the relationship in any way, and get the GPs on side with all of this. If it were me, the overnight stays would stop, now, too.

What appalling manners to slag off every aspect of a free holiday with your partner's family.
I get that some things might be annoying or disappointing or not as expected, and to mention it diplomatically wouldn't be a slight against you directly.

But to do it constantly seems really rude. It feels like she didn't want to be there at all. In which case he should be taken her away from the rest of you for most of the trip. Then at least you wouldn't have to hear her complaining.

So definitely don't invite either of them again.

Yeah, this. They're both awful for their behaviour.

I can't stand people like this who find fault in everything instead of the positives it just brings everyone else around them down and flattens the mood. Tell your son he needs to apologise to your parents and no don't invite them again until they learn to appreciate things more or he gets a different girlfriend

I also assumed they were teenagers until I saw your other post. Well, lesson learned. No more free holidays for these two.

I wouldn’t have her in my house again.

I feel for your DS here a bit because he was caught between his GF being unhappy about everything and his family who were paying for everything (which was, of course, completely their (ie the GPs’ choice). And that’s a horrible position to be in. And he didn’t handle it well.

They obviously owe the GPs and you an apology. But I’d let the dust settle a bit first. If she’s never been on holiday (!) then clearly her expectations were unrealistic and she’s out of her comfort zone.

I also don’t think your parents should be blaming you for their behaviour.