OP here. Minor point, and not really relevant, but he is my elder brother, not dad.
The inheritance which will be considerable will not come my way, but to his son and the new wife.
My belief on capacity needs more reading. But I think social services is certainly needed. But the idea of kicking that off really scares me.
Is it possible that he has made a calculated decision about quality of life vs side effects of his dementia meds?
Yes, that is clearly possible, although I find his denial of ever having dementia contractory to that.
I refer to my username!