Complex sentence: Gordon Tootoosis was raised with his 13 siblings in the Plains Cree tradition until he was taken from his home and placed in a Catholic residential school, where he was treated harshly and forbidden to speak his own language.
Split into simpler sentences: Gordon Tootoosis was raised with his 13 siblings in the Plains Cree tradition until he was taken from his home and placed in one of the Catholic Residential Schools. There he was treated harshly and forbidden to speak his own language.