Stephen King's Mercy adds Riggs and Courtney

From MovieHole: 

Chandler Riggs and Joel Courtney will star in “Mercy”, the Peter Cornwell-directed film adaptation of the Stephen King short story “Gramma”, says THR.

The horror pic, set up at Universal, “revolves around two brothers (Riggs, Courtney) who go with their mother to take care of their grandma. Unbeknownst to them, the grandmother is a witch, who made an evil deal using black magic years earlier”.

Australia’s Frances O’Connor is set to play the mother.