Their bodies were found Thursday morning in their Braeside home.
Derek Puffer, 35, has been charged with two counts of second-degree murder. He is the son of Powers' wife, Donna Lee.
Puffer has been ordered to see a doctor and officials say there may be mental health concerns based on his demeanour and interactions with police.
He is stepson to Bill Powers, who retired in October 2009 after almost 50 years in the sports broadcasting and communications business.
Investigators said a knife was found outside the home on the 1700 block of 110th Avenue S.W.
Officers were alerted to the incident after a passerby called police about a man on the street near Southland Drive and 14th Street S.W.
The man directed police to a house nearby where the bodies were found.