Honestly? Maybe subtly adding reality based news to their sources can help.
Somebody posted this docummentary in another sub/community the other day, and TL;DW: This guy's dad was a right wing nutjob, but his mom slowly unsubscribed him from right wing email, they moved which meant their new TV didn't have Fox 'news', and she slowly subscribed him to reality based new sources. It brought him out of his hatred and extremism.
When you take Fox 'news', right wing radio, right wing emails, and you dilute it with reality (NPR, AP, Reuters, Pew Research, etc), it can potentially help people break out of it. It's not easy, but it is a potential strategy.
So sign up your nutjob parents for email news letters from time to time, maybe it can help. Post real news in their communities on the offchance they see it.
https://www.pewresearch.org/about/follow-us/
https://www.npr.org/newsletters/
https://link.apnews.com/join/6nr/morning-wire-newsletter-footer-internal-ads