OP here. Thanks all for your insights and perspectives.
I do not want to, nor can I, explain the causes in ways that satisfy all viewpoints. Of course there are viewpoints, and there are facts. The facts/data support that A has clearly indicated, through repeated action (actually inaction, mixed with some action), that we are to expect nothing from her. However, she has happily accepted things from us, both material and not, in the very recent past (think 2023), while continuing her policy, and it is after many repeats of the same experience that my wife and I have agreed that, if we can expect nothing, then we are obliged for nothing.
It is possible that things could change, but that change will now need to come from the other side, as our repeated and sincere efforts have been met with negative and we can fairly consider them exhausted. But I do want to say it is not A herself that is the real problem. That relationship can be patched (it may take effort, which we have no problem with) if her spouse was not the way he is, so I want to disabuse y'all of the notion that I am so acrimonious toward the fruit of my loins, etc.
That's all I want to say on that matter.
On the house side, I did not think that through very much. I agree that it would need to be sold asap following our passing.
I need to think about all this some more. As noted, there are several new things you all have pointed out, and it is not a decision to be taken quickly or lightly. Once again, thank you all, and further comments are also welcome.