Elaine Leznoff, 66, died in the fire, which was declared an arson by the Integrated Homicide Investigation Team (IHIT).
IHIT said Friday that the injured boy, Kalvin Dosanjh-Leznoff, is not expected to live.
Dosanjh, 37. was estranged from his family earlier this month, and was not living at the home at the time of the fire.
Richmond firefighters were called to the home in the 10000 block of Cornerbrook Crescent around 2 a.m. PT April 13, after reports the home was engulfed in flames.
MAP: 10000 Cornerbrook Crescent, Richmond, B.C.