@oodlesofeep, it is clear that you have given this situation a lot of thought. Your question is not about the decision you've made, but rather how to discuss this with your family. I agree with @grammato3 that you may wish to seek support from a trained professional to help guide these difficult discussions with your family.

The Conversation Project has guides specifically to help you with these conversations:
- Conversation Guides https://theconversationproject.org/get-started

And from Mayo Clinic:
- How to talk about end-of-life care with your loved ones: Six things to consider https://mcpress.mayoclinic.org/healthy-aging/talking-about-end-of-life-care-with-loved-ones/

There are end-of-life doulas and social workers that can help with end of life planning with you and your family. While no decision has to be made now, you might find it helpful to talk to someone and understand what you might expect. Your local hospice may also be a useful resource.

When your doctors told you that without treatment, your life expectancy would be 5 years, should you discontinue treatment. did they also explain how the disease might progress and how to keep you comfortable to the end?