Aibu to be hurt?

I agree with @ABoldStatement.
It sounds very much as though your DP is very much on board with the arrangement and possibly knew you were going to be excluded from.the outset - if he hasn't got the confidence to talk to his own parents it very much follows he wouldn't have had the confidence to tell you the arrangements and so needs to put the blame on his family.

I honestly think you need to reassess your relationship. If you aren't married you are possibly in a much more financially precarious position and the fact you are being told very plainly you are not family doesn't bode well for you future together. Don't underestimate the message your DP is giving you about how he views you in his life.

YANBU for being hurt at this, not at all.

But YABU for not seeing that your DP is part of the problem here. Your DP is accepting what his brother told him and doesn’t feel comfortable checking it with his father (no mention of checking with his mother!!)? Bullshit.

And your DP is going with your child (and your DSS)? More bullshit.

Your DP thinks you should let this go? Triple bullshit.

If it was me and the above had happened, I’d be questioning whether your BIL is even the one that drew the line you couldn’t come and wondering if your DP didn’t want you to come and was embellishing that.

I’d be insisting on speaking to MIL and FIL about this directly myself, to know exactly where they stand.

And I’d be telling your DP he should go and stay with his family as of now given that you’re not part of it.

YANBU. My ILs did similar with DH, DH sister, and their eldest grandchildren. ILs were due to be looking after my son and dropped out saying they had another important commitment, apologies, so I had to take a day off work. DH was due to be taking our eldest DC camping. Low and behold they all show up in photos together having not invited me and little DS. So rude. No doubt their excuse would also have been about how they never get time together as a family. I was furious.

OP, if your DP is not willing to stick up for you on this, I genuinely don't think it bodes well for the long-term future of your relationship. I really would think carefully about maintaining a level of financial independence from your DP as far as possible. In particular, don't let any of your salary go towards the house or mortgage unless the house is in your name or jointly in your and your partner's names.

In the short term, I suggest you tell your DP that if he is not willing to speak to his parents about this, you are going to speak to them directly to ask why they don't see you as family despite you being the mother of one of their grandchildren.

Well not anymore really. Shit like that is like a hand grenade. The pieces don't fit together the same after

Is this holiday that you're excluding from replacing your own family holiday?

This is terrible behaviour from your husband and his family. Do you think it would be any different if you were married? Also curious as to why you're not married. Is your DH trying to protect his assets by keeping you sidelined? Are all unrelated females in his family treated as household accessories and grandchild incubators? Yes, I'm extraopolating massively, but the fact your husband sees no harm in this holiday arrangement indicates that you are not valued.

Your partner is horrible LTB he doesn't like you

I too can understand that for a short time, it’s almost like trying to recreate ‘the olden days’ when it was just the nuclear family, but you can’t get that back ever - there are now grown children, their own children, those days are gone. So yes, a meal, a few hours I understand.

That's so out of order.

Your dp needs to step up and make it clear you are family. You’re the mother of their grandchild ffs. If my dp didn’t either fix this or refuse to go he wouldn’t be my dp anymore.

No you aren’t great. This is not normal.

While he is on holiday you need to start collecting bank statements and contacting solicitors.

No decent person would be ok with this, how could you ever forgive it.

U OK, hun?

I'm trying to think about this. I would like the opportunity to see all my kids on their own now and then, just for old times' sake. But in that case it would only be for a short duration, say a meal or a day out, and I wouldn't be asking their kids to come along too.

Wow, that is really really hurtful, ouch.
I'd expect my partner to say his family (you included) all go together or not at all.

Then I think I'd probably not put in much effort with the family much anymore because it seems they don't feel the same.

Can you go and have a fabulous holiday yourself with/without a friend or friends? I'd do that. I'd probably cruise. But I'd not be able to feel the same about any ils.

Could it be your partners siblings behind this? My DP is one of 3 boys and in the early days of dating he had one brother who was horrible and if he didn't have a girlfriend himself always tried to exclude me from family stuff. It all changed though when he did get a girlfriend.

So thats why I'm wondering whether it's one of the siblings?

How long is the holiday for?

How far away is it?

Edited to add that my DP always stuck up for me though.

I had something similar happen last year.

I lost my shit with DP as he seemed to think it was OK for him and our child to play happy families with his parents, siblings and BIL.

After a “robust” conversation he realised how selfish and excluding his family (and he) were.

We ended up having our own break whilst the ILs were away together.

The damage has been done and, whilst I was never the biggest fan of ILs, I’m very cool with them all now.

In your shoes I’d be incredibly hurt and angry. You need DP onside to realise how hurtful this is to you and he should be standing with you. If he doesn’t, then he isn’t a partner, is he?

I would make it clear to DH that you’re hurt. And if PIL ever ask, I would make it clear you’re hurt to them too.

And I would quietly stop treating them like famiky. No more hosting or help or presents or cards or posting pictures to group chat.