Then they perhaps contacted or were contacted by a right to die group and slowly descended into the belief system which was necessary for them to accept, in order to pursue what would allow them to financially survive.
I think this husband, Schiavo, has followed much the same course, except that in his case it may have begun less from financial needs and more from emotional needs.
Principles of cognitive dissonance show us that people need to believe in a certain way to justify their actions. Additionally from cognitive dissonance we learn that -
"the more difficult it is to get on a course, the more participants are likely to value it and view it favourably regardless of its real quality."
and
"the more obscure and convoluted the subject, the more profound it must be."
I am assuming here that it must be difficult to come to the decision to kill someone you once loved, no matter how cruel you are as a person, and that death can be considered an obscure and richly convoluted subject.
Therefore once these family members make the leap to accepting the idea that their relative deserves a right to die, they then become advocates for the movement itself, and among the most committed.