A Sense of Shadow — Kate Wilhelm

THEY CAME TO HIS DEATHBED. FOUR DUTIFUL CHILDREN.
Each the child of a different mother. Each mother the victim of a tragic accident, unsolved murder, mysterious disappearance.
As he sank away they glowered their hatred. It was a hatred he expected, and his revenge was well-planned.
He left a multimillion-dollar legacy, bearing a ghoulish price tag. They could pay with their sanity, or their psyches, or their souls. They would be part of an experiment... something to do with brain waves. It would be
a great service to science, they were told.
Just one last little joke on his kids, and they swore they could hear him laughing ... all the way to hell.