What I meant was that Mrs. Finn would not have killed her child by withdrawing a feeding tube under any conditions. But there was money at play in killing off the husband. I believe in such cases blood is thicker than water (marriage), particularly in light of the high divorce rate. Obviously I was stating an opinion.
And obviously you are entitled to hold any opinion you wish. However, any opinion only carries the weight of the reasoning and evidence which support it.
There is no basis in reason or evidence to suggest that one would be more or less likely to withdraw artificial life support from a person of a particular age or relationship. Clearly, it is the degree of debilitation and likelihood of recovery which informs such decisions, not the age or station of the subject.
There are probably people (and you apparently are one) who believe that biological relationships are stronger than volitional and legal ones. I do not. I happen to have had two children: one biological and one adopted. Both are now adults. I can assure you I do not love one more than the other. Moreover, I can assure you that I loved my wife as much or more than either. I do not believe I am unusual in that respect.
That's the problem with your theory.