After their parents died, their grandparents raised them.
Literal
Parents [subject-が] died after, grandparents [subject-が] them [object-を] raised.
亡くなった後 (after dying) uses the respectful/euphemistic 亡くなる for death instead of 死ぬ. 祖父母 (grandparents) is a formal compound: 祖父 (grandfather) + 祖母 (grandmother). A straightforward narrative of family circumstances.