Hoarding/ Clutter/ Filth....
Well I gotta say I am on the "if it isn't on your property or harming you, leave it be." if it is garbage/ filth, yeah you got a case, but you do not have the right to tell someone how to live their lives and how many non running cars/ projects they can have.
As for hoarding, well there can be a case for that it can be dangerous (read a story of a guy that had so much stuff stacked in his house/ apt that it fell on him and he died and was not discovered until weeks or months later) Family can help with any intervention that may be needed.
Where I am at right now, I have ADHD so clutter is the norm lol I have a lot of stuff, and running out of places to store it for it to sit unused for years. I have been slowly getting rid of what I will never need and freeing up that space. I got a small box of Buick Lucerne parts that I am going to rehome as I will likely never get another Lucerne, a good friend has an uncle with one so I will give them to him. got many totes of Ranger parts, will keep those. got a lot of good stuff off of Rock Auto Clearance. I do have a walk behind 33" commercial mower with all the trimmings, has an aluminum grass catcher, mulching blades, etc that is taking up space in my shed. will need to get rid of that. As for my two sons and who gets to clean it all out... the oldest will likely not even have anything to do with it as he has drank the Kool Aid his useless mother served (another story for another time) and the youngest will likely want all my tools and Ranger, the other stuff that I have collected he will probably just chuck, but hey after I am gone, that will be his prerogative.
My thoughts on heirs. my parents have done a great job of getting rid of their stuff, and given me and my sister some of the family stuff that is passed down from grandparents. beyond that, when they pass I think me and my sister are going to do an auction of the furniture and personal stuff that we do not want then sell the house. and I think this is a good idea for those that are looking at a huge amount of "junk" to do. auction it off. grab the stuff you want before hand and let the auctioneer get rid of the rest for you. you might not get as much for it as it is worth, and you have to pay auction fees, but it is an easy way to get rid of it and get a little cash for it as well.
My thoughts anyways.
AJ