Yeah, agreed. If it wasn't specifically the process of packing, maybe they've already discussed the bag situation to death or Grandma showed up uninvited to do this. I have so many questions.

I mean, her son could just be a dick. But I have a few family members who try to buy control over others and any disagreement story that starts with 'I spent SO MUCH MONEY on them' is a giant red flag to me. If the holiday was so expensive and it's just an extra bag standing between you and enjoying it, any reasonable person tries to make that work even if only by commanding that all teens must be able to carry their own stuff and put their backpacks in their laps in the car or something. But if on some level you thought you were purchasing something more intangible than a cruise, this makes much more sense as a hill to die on.