My wife and I both use the same keycard. When I have gone to level up/check in without her, they have refused to give me her pack, and told me that she needed to be present with me at the time. But I have also read reports of people being asked by the CMs to only have one member of their party wait in line.
Doesn't that just seem stupid?
I can't see, especially if you share a keycard, why everyone would have to go? I can understand them wanting to know that the ticket has been used to enter the Magic Kingdom, and not that you've taken everyone's tickets and they're all still back at the hotel (the same as the current Fastpass rule), but I can't see any reason why everyone would have to be there? Wouldn't it just take up more space in the building?