Hey there, it's a tough decision there and only you know best. I'd make sure to have a second opinion to make sure I hear the facts from two separate doctors-- you never know!
You are correct that probably 90% of your family will not understand your decision if you decide to avoid treatment. They all want you to stay around, and I'm sure they will try to change your mind here and there. I'm a firm believer in doing what works for you, and sometimes treatment is not in the cards. Just weigh your options, and if you see any glimmering hope/possibility in the treatment give it a good night's rest before flat out saying no :)