Omni-Man, Mark Grayson, Debbie, and Cecil are voiced by J.K ... The latter is defined by the performances of their voice actors. All the main members of the cast are listed here.

Debbie Grayson didn't die in Invincible Season 3. On the othe hand, the comics from which the show has been adapted don't explicity mention the cause of her death, hinting that she likely passed away ...