V2 P5
35% In fact, all of the children inside were Melulu's stepsiblings, born from different mothers. ... Wolff maintained relations with many women and bought their babies from them when they gave birth.
Are they step-siblings, half-siblings or adopted siblings? Step-siblings are children born of two different families who have been joined by marriage. Do these kids all have different biological fathers and mothers, or do they all have Wolff as their biological father? If so, they're half-siblings.
Update: Later in the chapter, I see And as always, the faint sound of a woman’s moans filled the air. Wolff summoned women to his estate on a frequent basis to further add to his already absurd number of children. Seems like they're half-siblings.