Game obu Familia – Family Senki

The protagonist along with his step-mother, and 2 step-sisters(step-aunts) are summoned into another world where demi-humans are the rulers as saviors, but its not to fight against a demon lord, its to fight an Undead Apocalypse monsters called “Dead Mell“ that have overrun the world and that can only be killed by using weapons made with holy silver.