So, you want to give your step-mom some of your inheritance. Very generous.
However, what's wrong with getting your full inheritance and giving her or the daughter with MS money later if they need it?
Giving money now runs the risk of being lost if she re-marries badly (to someone less than scrupulous), or if she has imperceptible cognitive decline and gets scammed out of the money.
You can just retreat to the position of "Upon reflection, I realize we need to be doing things as dad specified" and "following his wishes".
However, what's wrong with getting your full inheritance and giving her or the daughter with MS money later if they need it?
Giving money now runs the risk of being lost if she re-marries badly (to someone less than scrupulous), or if she has imperceptible cognitive decline and gets scammed out of the money.
You can just retreat to the position of "Upon reflection, I realize we need to be doing things as dad specified" and "following his wishes".