One easy way into the conversation if the family member is more conventional: being in ketosis usually improves the efficacy of standard treatments. For someone who is willing to go down a rabbit hole, I've seen lots of positive references to Paleomedina. I don't think they list cancer on their website but I've heard several folks mention that the main dr in that practice has had success with remission for patients who are willing to go all-in with her dietary suggestions.

In any case, I'm sorry, Holdonaut! Best wishes to you and your family.