I went through this in recent history. My mom has been a JW for most of her adult life, along with my father. They raised me in the truth, but as a teen they faded a bit and then came back strong in my early 20's. Because I married a girl in the truth, I was strong until my mid 20's when I began to fade hard and fast. And while I continue to have friends and family in the truth, I have transformed into a person, who - beyond a doubt, knows this is hogwash.
So when my mother was in ICU, and the nurses told me she would not make it through the night without a transfusion - I learned all the "alternative treatments" were nearly useless when you get down to a certain level.
I talked my Dad into going home for a while, to get some rest. He is old and suffers from his own ailments, I told him I would stay the night but that I needed him there for me in the morning so I could rest.
After he left I explained to my mom that when the Bible authors wrote abstain from blood - they were talking about the pagan cow worshippers that were drinking blood and dying from it. Those authors never envisioned a day when blood would be transfused and lives would be saved. And then I told her how the Society has known this for a long time, but if they were to reverse their position they would leave themselves open for a flood of wrongful death lawsuits.
And I told her that Jehovah wants her to live, to help her grandkids and continue being a good example for this family. I couldn't stop crying, and I am not a soft man.
And somehow, something I said took root. And she said ok, and the nurse came in and we filled out all the paper work and I had them remove any hint of the word "Jehovah's Witness" from her paperwork, because I told mom that when they see that, they see "GIVE UP". And that night she had a transfusion, and she lived.
And slowly my father understood what happened, and she told him my reasoning. And while they hated to admit it, they realized I was right.
And her sister, a another lifer, is suspicious, and elders showed up the next day - and I explained to them with tears in my eyes and my fists balled up at my side in a subtle, non-threatening way, that this was a family matter and they were not welcome here.
And maybe it's because I am known to be possibly crazy, like my father, that they have left us alone.
And if they ever try to DF my elderly mother, I will threaten a lawsuit and call a lawyer because it would devastate my mother and there is no need for her to ho through that.
So, stay strong and do not be afraid to say what you need to say, just be smart about it - and discrete. Have faith that God will help you with the means and methods.