Why would you be helping an elderly parent arrange their affairs? There are a lot of issues in doing this. They are grown up and should be able to do it themselves. Unless they have Alzheimer's. But if you "help" them, those around you will be affected. "Did you add something to your pile that I wanted?" "I see how it is. You're trying to get all of the good stuff!" I would be more careful with your other family members, unless your an only child.
But in helping someone with the affairs, just gather everything they own and put it in front of them (on paper, in physical form that might be a lot). Let them be the judge of who gets what. But they have to know what they have first.