I'm so sorry you are going through this OP, but yes, no matter how hard it is for them your family should respect your wishes as long as you are of sound mind and not being forced into the decision you are making.
On a personal note, a few years ago my MIL was diagnosed with Multiple System Atrophy, a disease which causes lesions in the brain, causing different parts of the body to be affected, depending on where the lesion appears (basically kills your brain off, but normally slowly so your body packs in over time.)
MIL had always been a vibrant, active part of the community and all of a sudden her body was rapidly failing. Everything from walking to talking to eating to toileting was affected. When she could barely do anything she had a 'Do not resuscitate' (DNR) put in place.
It was heartbreaking for her friends and family, but us not wanting the DNR was actually selfish on our part, as it would have meant we had her for a few more days or weeks, rather than taking into account her pain and misery and her not wanting to be in that situation anymore. We never told her we didn't like her decision, just supported her. This is what your family should be doing, but I guess they are upset and possibly in shock over your decision. They are thinking about themselves and the fact they will miss you, they need to start putting you first in this instance.
My MIL could barely eat by the end, a spoonful of ice cream a day for the last few days, all her meds were liquid as she hadn't been able to swallow pills for a while. Because of the DNR she couldn't even be put on a drip to feed her and she grew weaker and weaker until she died in her sleep on Boxing Day morning last year. She was on lots of painkillers, but they never really took all the pain away and she felt quite humiliated by not being able to do all the things we take for granted and having someone else sort every bodily function for her, her dignity was taken away from her by the disease. Had we fought to keep her alive for longer we would have been prolonging the pain and humiliation, we would have been selfishly keeping her alive for our own needs and not hers.
You are refusing to go on a ventilator, you are not refusing all treatment so haven't 'given up' (sorry, can't think of a better way to put it, my MIL hadn't given up, there was just nothing that could be done to improve her health), but I can understand you don't want to end up on a ventilator for the rest of your life. Your family might take a long time to come to terms with your decision.
I recommend you have your choices put into place legally so your family can not use the courts to overturn your decision. They will also have to grieve over this decision, could they get some counselling to help them come to terms with it?