I would like to offer a suggestion:
To begin with, clear the house totally one room at a time. For example, the living room. Take everything out and place in covered trailer — throwing nothing out. Line as much of the room as possible with shelving. Involve the homeowner with no more than two people at a time, and stock the shelves with things that absolutely cannot go. Keep the atmosphere friendly and calm. Perhaps have some music playing. Laugh as much as possible....move from room to room following this approach. In my opinion the homeowner feels totally overwhelmed and disrespected. I think if guidelines were set, ie, set out areas where nothing can be placed such as leading outside for fire safety.
I know this would be very time consuming, but perhaps could be done without breaking the homeowner down.