That's exciting. Hope you and your husband have a good time doing whatever you want to do.

And honestly, I understand how you do not want to punish your oldest child for nobody taking your youngest with them ever, but I really think you should say something. Especially if it is family. If it was just a friend with a child close to your oldest, it would be a different story. But, I really do find it sort of rude that family members of yours would only take 1 kid all the time and not the other ever.