If multiple characters with gold have the same keyword, each Fool character with gold will only gain one instance of that keyword.
Each Fool character with gold also counts itself when checking whether a character with gold has a keyword. That means Shagwell will give Fool characters with gold a second instance of any keyword they already had.
If a character that was giving two or more Fools a keyword via Shagwell's constant effect leaves play or loses that keyword, those characters will lose that keyword too, unless there is another "source". They cannot continue to be each other's only source of that keyword if none of them are gaining it from anywhere else.