Books are hard to get rid of IME. I was quite ruthless a couple of years ago and surprised myself by donating reference books rather than novels, on the grounds that reference books go out of date and their contents can be searched online very easily. Unfortunately I have accumulated more since then, so am going to have to have another purge soon.
The biggest problem we will have is the garage, which is crammed with power tools and similar. Mr D has an unfeasible number of the things. Plus whole cabinets of screwdrivers and spanners. He rarely uses them, although he recently fixed something for DIL, so the odd one comes in handy now and again. I have no idea about any of it, and if he goes first I don’t know what I will do with it all. Neither son nor SIL will want any of it (and daughter and DIL won’t give any of it house room), so I’d either have to pay to have it all taken away or put an ad online for people to come and take what they want. I wish he would sort it out, but (a bit like me and my yarn) doing that would be acknowledging that he’s coming to the end of his usefulness, which I don’t want him to do.