I'm afraid I can't help with the CHC stuff, but, for what it's worth, we're in a similar situation, with Mum having dementia and cancer.
My mother has always been one of those who says you should fight for life as long as you can. She is, on principle (while not 'hard-line'), anti-abortion and has always believed that life support should be kept on until some time after the medics say it should be turned off. However, in March of this year she was given the diagnosis of oesophageal cancer. At the time, she still had considerable capacity to make her own decisions and she surprised me when she said she wanted to be DNR. I have to say, I'm pleased she was able to make the decision herself, because - knowing her past attitudes - my brother and I would probably have said that she wouldn't have wanted that on her file.
My point here is that, given the history of your family compared with ours, it is pretty obvious to me, on the outside, that you have made the right - albeit difficult - decision.
Keep strong!