Spawning Pit once for each creature you control by sacrificing that creature.
Resolve all
Spawning Pit abilities, putting a charge counter on
Spawning Pit each time.
Resolve
Dualcaster Mage's ability, copying
Living Death.
Resolve the
Living Death copy, causing each player to exile all creature cards from their graveyard, sacrifice all creatures they control, then put the exiled cards onto the battlefield.