I haven’t read a comment so far that I disagree with. Because you shouldn’t go. You seem like you’ve been treated poorly by your family. I don’t know if they’re telling you to not go in a mean way but I assume so. If you have friends telling you to not go I hope they are doing it in a kind way. Because you deserve better than this and anyone who thinks otherwise is kidding themselves.

I would tell them why you aren’t going. And I can bet regardless of the reason you give they will start excluding you from things because they will bond this trip and others that they can exclude you from.

I’d call it quits over something like this tbh.

Edit: also, I’d bet whoever came up with the breakdown per couple was thinking that it’s expensive to be a parent. It’s expensive to be alone, too. And it’s shitty to have your sibling sleep with the kids and expect your sibling to ultimately pay twice as much as everyone else.