Not at his best? Belongs to the greatest generation?

Recently, a certain righteous man was killed, whom many considered to be the greatest of his generation or other distinguished figures.
In recent years, he has even given practical instructions to the public, in a variety of areas.
Which were, how to put it gently? Not really acceptable to many intellectuals.
Immediately after his death, many rich people wanted to buy his belongings, such as the stand or manuscripts, etc.
Price: Many millions in dollars for the items, a business for the rich who see it as an interest. (It was reported that the stand sold for $7 million)
In the last 9 years, one of his sons moved to live in the house of that righteous man and everything was conducted under his auspices. Of course, even the shopping after his departure, throughout the country, is done through him, he lives there.
According to what was published, the other brothers cried out, “Where are we?” and demanded that the brother who lived there share the inheritance with them.
He, in the courthouse in Bnei Brak, issued a letter in which that righteous man bequeathed to him everything he had…
The date: 9 years ago, when he moved in with him and managed everything.
The brothers cry bitterly, for it is known that by then our father was already ‘not at his best’ and this will is invalid and he must give his brothers their share as usual.
It’s a mess. (SCC is really big money)
 
My questions:
1. An object used by a righteous person. Is it permissible to buy it? To pray to this standar? To just keep it as a virtue for protection?
2. Is it permissible to say about a person that in the last decade of his life he was ‘not at his best’? Is this insulting? Is this a disrespect for the Torah?
3. Since when is writing a will not considered real property? That a person is a little tired? A complete fool? Doesn’t understand what exactly is being said or told to him?
4. Do his halakhic and ideological instructions have any validity in those years?