How old are your parents? If they are retired, that might explain a lot. People say you become broad minded, wise and knowledgeable if you have ample time to read and educate yourself, instead of working more (that's why many people say society's obsession with work is a distraction tool to prevent people thinking that the system is rigged). However, it also goes the inverse towards extreme radicalisation.

I don't have a practical advise to give to de-redicalise your parents, but typically radicalisation is not just you have too much time to consume so many contents, but also loneliness is a factor which most people overlook. Hannah Arendt made a conclusion in her book, Origins of Totalitarianism, that loneliness is a precursor to totalitarianism. The far right (and far left as well) sell the snake oil that only they can bring people together again.

A lot of old people who are lonely are vulnerable to extremist propaganda because their minds are not in the right place. This is something to consider imo when you have to interact with your parents. Genuine human connection is the missing ingredient. A friend of mine has also become far right. He moved to London many years ago, and my guess is that because big cities tend to be individualistic, this made him lonely. The far right rabbithole created a sense of togetherness and purpose for listless individuals.

Edit: wording