Who would have legal right to car when mother dies and leaves car to sin in suicide note son verbally and physically gives car to daughter but son still has title?

I don't think anything has changed. Son owned it prior, note may/may not be valid (due to duress) but even if so states what is already a fact son owns and registration will match title so unless she is on both as a co owner he can get the car wether she want to give it up or not.