Manga Game Obu Familia - Family Senki

The protagonist, along with his stepmother and 2 half-sisters, is summoned to another world where half-men are rulers as saviors, but this is not to fight against the demon lord, but to fight the Immaculate Monsters of the Apocalypse called "Dead Mell," which flooded the world and which can only be killed with weapons made of holy silver.
To do this, a family is created (a group of 4 people) in which they are a sword master using a holy sword, a keeper using the power of the earth to protect, a healer using the power of water to heal, and a black magician using the power of fire to destroy.
The role of the keeper, magician and healer is to support the master of the sword, who can only kill monsters.

But in order to use magical powers, you need to sacrifice part of your being in order to conclude a contract with the spirits, and the higher the sacrifice, the higher the power. Now they must choose which of the three must sacrifice part of their body to gain power, and who will possess the sacred sword.