When we did work on our old house it required the attic to be decluttered/sorted.
Four of us and many trailer trips to the tip, trips to charity shops.
My kids are older so helped us which was good, they had a say in what was kept as most of it was their old toys etc.
Dh up the attic passing stuff down, he sorted what he wanted to keep of his when he discovered it.
Me on the landing, sorting what was staying and what was to go out of the house.
Kids running stuff to dining room (where I had set up boxes) or to the trailer which was outside ready.
Essential, dry weather
, bribe of a takeaway for lunch and tea 
The feeling when it was all over was IMMENSE.
Our workman couldn't believe it was the same attic and when we came to move house a few years later getting everything down was much easier as most of it was all sorted and boxed up, we'd dumped some more up there but nothing like it was.
Most of my dining room was used to store our attic boxes ready for moving day, I mean floor to ceiling, only room for table left no room to sit around it.