When Ketheric Thorm became an immortal monster, the rest of his family followed his lead. As players of Baldur's Gate 3 explore Reithwin in the western half of the Shadow-Cursed Land, they'll come across three members of the Thorm clan who are lording it over their twisted undead minions.
Baldur's Gate 3: How to Defeat the Thorm Family Without Combat
Ketheric Thorm brought his whole family with him into undeath, but Baldur's Gate 3 players don't have to fight them to beat them.