My parents didn't exactly hoard, but they were both born around WW2 and have the accompanying mentality; they like to be prepared, and they like their hobbies. This changed about 10 years ago, when my mother had a health scare, and my sister declared herself extranged from them and refused further contact (they reconnected tentatively about 5 years later).
My parents have had a few more health scares since then, and have declining health. The 'Home Assessment Assistant' from the health insurance company (specifically dedicated to falls prevention and longer independent living) advised them on removing a large number of items in their home, which they have done. Every item they discussed, I would get facetimed and asked if I wanted it. The answer was usually 'no'. Now, every time we visit them for a weekend, there is a dedicated shelf in the wardrobe with items they are getting rid of, and I can help myself to any of them. Items I don't take, I put in a box or bag next to the front door, which is the dedicated 'out' position. They will then take it to a charity shop or auction house; until it actually leaves, all visitors will be asked to peak in the box or bag and take anything they fancy. They started by getting rid of most of their books, my mother's pieces of fabric, and my father's miniature trains.
My parents also used to volunteer to help any older church members that had to move into elder care. Any items not moved, they would help relocate. Sometimes by throwing out, sometimes by adding to the church garage sale, or selling on specialised websites (all profits to go to either to elderly person or the church). They enjoy relocating stuff, they enjoy adding to their home decor for a while and then moving stuff on, helping people.
They have not read, but definitely have the 'Swedish Death Cleaning' mindset.