Nobody's been unkind about these three, some people have pointed out truths about one of them, expressed an opinion that the aristocracy is not perhaps such a good thing and nobody has said anything untrue about the Duchess of Kent. Apart from the people who can't tell her apart from Princess Alexandra, that is.
People aren't critical of them "just because they are Royal", that's an odd thing to say.
And "venom"; extreme malice and bitterness shown in someone's attitudes, speech, or actions. If you want to see venom, take a look at any thread that mentions Harry and Meghan.
True enough about people being unpleasant at heart though, but not the people you meant, I suspect.