Attacking delusions head on tends to create defensiveness, so I tend to walk around the issues, I might be minimalist in conversing about them and suggest other alternatives without insisting. Mostly the person needs to let it out .. but when I feel too put upon I might start moving around or suggest going for walk or doing something ..eg., day in the country ... if they have capacity at that time they might respond thoughtfully and tone down a little and appreciate the company and togetherness. Sometimes silence ... and I am there for you .. is best.
I never agree to anything I dont think is true but try to be diplomatic.
I focus on the creative and productive traits in the person ... my sister was a great sewer ... my brother a leadlighter. I was not allowed to talk to my father and most I discovered about him was through reswearch of public records well after he died.
It was not enough in their case as our family was too dysfunctional as mum was too defensive and often messed things up with her rigidity of thinking but she also tried very hard in her own way .. we were just at the bottom of the socioeconomic heap.
I listened to a lot of husband's rants about the CIA and PSI phenomena and tried to interject a few rational points here and there. He had more confidence in his "science" as his whole family was highly educated and I was the only one in mine at that time, but I did know the basics. He made a DNA dodecahedron out of kids toys and then twigs from a bush walk etc .. I always encouraged expression and creativity. His things were writing, sculpture and painting so that was what I supported. He was pretty arrogant about it all which was very wearing, but it did help him get out his demons. The artwork was very black and I didnt really like having it on my walls but it helped him .. gave him social opoortunities to talk about his art etc it was just the way it was then.. I put a lot of support in many therapeutic art works for him ... for his part he appreciated my qualifications and intellect ...for a while ...I am only sorry I could not save my brother and sister .. but I do think it is the way to go.
If people havent found a preferred outlet then that is the challenge to guide and provide opportunities for them to discover something ... whether it is being in touch with nature and knowing all the edible plants .. find a passion ... and some meaning can develop.