One helpful thing to keep in mind as a retort-stopper is that you won't "win," you won't change anyone's mind, you won't change any votes, you won't make the atmosphere in the room any better, YOU won't feel any better.
Carolyn HaxYou can't make people like you under the best of circumstances, and you certainly can't make them like you while you're actively badgering them on what you perceive to be their failures of conscience.
Carolyn HaxPlan your own vacations when you want to, and plan a suitable combined vacation with this other family when you want to. If they freak out at your planning your own vacations as you see fit, then let them. Bowing to unreasonable demands because someone will make you pay emotionally if you don't is not a healthy option.
Carolyn Hax