My husband had surgery last December. He was hospitalized for a few days. During that time my daughter-in-law (whom I hardly know) took over and would begin talking to the nurse while I just stood there with my mouth open. I didn’t want to say “uh, I’m his wife” because it would have caused a problem with my son (she’s only trying to help, don’t ya know). I told this story to my sister and her daughter not long after. My niece said, well after people get to a certain age they kind of disappear!
I will be 70 in August. I’m perfectly sound of mind. I’m able of taking care of myself. My husband can run rings around most men in their thirties. We call him the energizer bunny. He also has all of his mental faculties. I don‘t know your folks but I know that if my kids came to us to have “that talk” I would be insulted. What we do with ourselves is not their business. Perhaps we have planned properly or perhaps not. If not, into each life a little rain must fall

hope they are ready for it. As it is we are getting rid of a lot of things, clearing out closets. Giving away things (lots of books) and throwing out other things. We have never been what you might call pack rats but we do have some superfluous stuff around. We are making the decision ourselves that we would like to move closer to the grandkids. Once again it’s our choice. As I see it, as long as one parent has his or her mental faculties I suggest that you treat them like adults. If one of mine started treating me like a child (very disrespectful) I’d let him know in no uncertain terms that he is out of line.
After writing the above comment I went back to read your post again and would like to comment further on one paragraph “My brother and I have discussed having the elder care, end-of-life talk with mom, but, though I love her dearly, she is a dragon lady with a lot defense mechanisms and a healthy does of pride couple with the usual fears of aging; loss of agency, feeling of uselessness, etc.”
I must say that that paragraph comes off as unmitigated condescending pride. Why ever would a loving son put his mentally and physically capable mom in a situation that would cause her to be behave defensively. Seems that your mom is nicer than my sons" mom because this one thinks that a good defense is a great offence. End-of-life discussion INDEED. Have you measured the curtains?
Annie