I've been thinking overnight and while some messages have felt brutal, they have given me the perspective that I needed, thank you.
My original question was whether I was right to be hurt, or was I being oversensitive? Our family dynamics are that I always suck up the shitty decisions that hurt me because if I ever dare to raise them, I'm told I'm overreacting and too sensitive. As a result, I stay quiet but I hurt. This is one in a long line of things to happen, and these have clouded my judgement. I needed perspective and to see things from their point of view, which I've now got.
A few posters commented on the new date - I know their closest friends had input in the new date. Other friends were also told before us at a BBQ, while we were told via a group message that updated the rest of the party. I think this set the tone a little for me that we weren't part of the critical 'must be there' list, but the 'be good if you could make it' list.
However, there is an awful lot of judgement at my reasons why this isn't doable for us. There are many factors but yes, of course, cost is one of them. We were prepared to spend thousands on going (it's not a destination we would choose otherwise), but to add value, we'd stay on and make it a family holiday. However, the costs for a week are crazy and we can't extend because of the new date. To give some context, we were looking at 2 weeks all inclusive for £8k - this is not an amount we'd spend on a holiday but for a special occasion we agreed to push the boat out. For a week, the cost is £6.2k. Surely this is a staggering amount of money for a week's holiday? And, courtesy of Covid, our finances simply aren't in the same same position as last year and to go, it would mean a lot of sacrifices, but had it been the same dates which meant better value, we'd have done it even though the prices had gone up a little.
As for the kids school, they're both in important secondary years. While there aren't exams this year, that doesn't mean time out of school wouldn't have an impact. How the flights are scheduled would mean missing a full week plus the next Monday (we wouldn't get home until mid-morning), and then going in on the Tuesday jet lagged. One of the DC really struggled with the worry of 'being left behind' during home schooling and even a day off sick makes this anxiety shoot through the roof. This is why I'm not keen on taking them out.
However, having said all of that - I do now understand that to DB and his GF, it could look like we just can't be bothered. Or how we weren't prepared to make sacrifices to get there. They don't have kids so the concern about taking them out of school perhaps wouldn't occur to them, and they've often commented that they forget that for us, costs are much more when we factor in the children. I'm going to call him and talk it through and just explain our thinking. They've said before they often forget we have to pay double to include the DC, so may be forgetting the cost element, and also the impact on the kids being out of school. We won't talk about whether he cares or not - we don't talk like that. And having though of things overnight, I say we're 'close' but actually, I don't think we are.
Thank you all again for your input and helping me see the bigger picture.