Partners mum is going to die tonight but im meant to be taking my kids on holiday tomorrow

Sorry for the difficult situation you're in. Though a few things to think about - would he do it for you if the shoe was on the other foot?
You've looked into costs of flights and you're going to lose a lot of money and ruin an expensive pre planned family holiday if you cancel it
Is she guaranteed to die tonight? (sorry if that sounds crass, but often people at end of life can keep going for longer than you think)
What would cancelling achieve when your partner already has support around him?
I would just go, offer remote support, speak to him when you're able to and offer to come back if he needs it. Chances are he'll manage the situation on his own.
Don't disappoint your kids or put them under pressure to go alone through US immigration, it's stressful at the best of times. Good luck with whatever you decide

He is right
100% travel as planned. Dont come back early

Its unfortunate but your primary obligation is to your children.
Anything else would be grossly unreasonable to them

In the uk funerals take an age (fil was sped up and took almost 4 weeks) so you will be back from the holiday for the funeral itself and also be there to help with other aspects when you get back.

He can cope. He isnt alone - they are people who can support him temporarily

Different circumstances, OP, but when my partner's father and mother died 400 miles away I wasn't there because of work and other commitments. My partner never suggested I should have been there and there is no bitterness involved. My in-laws were family-orientated and had all their children and grandchildren and extended family around them in the days before they died. I think I would have been and felt very much like an outsider and actually required support from others.

Find out what your partner thinks. It sounds as if the circumstances are very different but this may be a time when he'd just like to be with family and doesn't want to have to be concerned about you.

You also seem sure your DP's mother will die tonight, but people don't necessarily die when expected. A friend whose mother had a terrible fall and major bleeds into the brain last week was expected to die within 48 hours but is still alive today, seven days later. You will need to factor this into decisions about sending your children to the USA on their own.

Agree, he's not her husband, her kids are her family, he's her boyfriend. Family comes first.

Take your kids. Explain to your family what’s happening. Then return home and support your partner if he needs that. Then go back and collect your kids.

Go to America with your kids. Your partner will be fine.

He will be in a whirl of family stuff and practical organising of funerals and the like for the next 2 weeks. He will really need your support when all that has ended. You often don’t really have time to process what has happened until after the funeral when everyone else has gone back to normal. Be there for him then when all the others have moved on.

Could you go with your kids for the first week then see how he is and if he wants you to fly back for the second week leaving the kids with family over there- if they’re all comfortable with that?
The first week he might be too much in shock/busy with kids/arrangements and not have as much need /time for you as when it starts sinking in? Or by that point he might say he’ll be fine, stay the second week and he’ll see you when you’re back.

Exactly this. He can cope on his own. Women have to cope with a LOT of shit on their own... As you say, he's a big boy. A grown-up. He can deal with this, without wrecking the OP's holiday. (And her childrens!)

The suggestion of going as planned tomorrow and then offering your partner to come back for a few days if he is falling apart sounds sensible to me. I’d be going to bed now as you’ll need your sleep.

Ive been supported by a partner from afar when a parent died. I absolutely didn’t want him to make the long haul flight out to help as was swamped with grief, and organisation. It was good having him on the phone and on my return, if it helps

What is this even trying to answer to. The bereaved are living. OP is not considering staying in honour of the deceased, she wants to support ehr Partner.

I’m nearly 40 and dread US immigration - they are mean, surly, abrasive. I have a no issue background with a normal British passport. I have once, at Boston, been taken to the “holding pen” and it was horrible. They detained me for an hour whilst my American husband had to wait in the baggage reclaim bit. He was not allowed to see me. I didn’t do anything wrong and it was entirely the officer in the passport stamp-y booth bit’s clerical error.

I wouldn’t want to be 18 and in charge of two minors in a US airport.

I would go on the holiday. He has his children and siblings for support. Your kids need you

I think you need to put your kids first ultimately op. Go on the plane. Support him from the US until you are together again.

He is an adult and has family and grown up kids etc.

It's not like your ex, as you do care and will support him.

There's no way I'd send an 11 year old long haul without their mum or dad personally, I just couldn't do it, regardless of what country they were landing in and who they'd be staying with.

Also, 11 is young. This is a big holiday for you and your dcs, and extended family, your partner should be able to tell you to go, even if it's not his first choice he should be able to see that your youngest especially is your priority.

This is a good plan.

You're the lawyer, but wouldn't extreme stress mean YOU wouldn't be fit to go, triggering insurance? Only saying as I know someone who was allowed time off work (missing something really serious-they'd never have let her take it holiday) because she got a sick note for stress. Like I say, I'm not qualified to judge on this, but might be worth checking.
FWIW, I cancelled a holiday once just to be with a friend whose dad was very ill, and I finished with a boyfriend (not using the term partner as feel he was only a boyfriend) who went to Spain when I was going through some serious stuff, because I would have been there for him the other way round. But people are different, there's no law saying I was right and that he was wrong. I just knew he wasn't right for me. It is only opinion.

If you lived together I think it would be different but you don’t. He will have family to
rally around him while he grieves. He might even need space. It will be very hard to speak to him about this now as I imagine he won’t be in a place to talk about it.

Life is for the living and all that jazz

i feel for you. Very shit choices but this. Take kids to America. Once they are safely with family you can decide if you need to come back or not and you can leave them with family if you need to. You will have more information in a few days to help make a decision.

Why does being married make any difference if you've been together 8 years?

Thinking about this realistically: your kids are going.
They cannot go through Immigration alone. Not under those circumstances.
Therefore you are going.
Everything else will slot into place from that.

Good luck, this is shitty.

Ok based on your updates then I'd say if you can't get the airline to reduce the charges so you can fly with kids on Sunday you should go, deposit your kids, do some family reunion stuff, and then fly back early. And speak to DP and see what he wants when you get a chance, and that will probably help you make the decision.

Alternatively could a friend/relative fly out with the kids to take them or one of your US relatives fly this way to collect them? That way if there's hassle at US immigration they will have support. On the way back into the UK it should be much easier.

I would still go if I were you @Allcrisisnocalm She's his mum not yours, and you're not married. I gather the children aren't his?

Then I think I’d send them alone. They’ll be fine.