Use 'adoptive' to emphasize the meaningful bond in relationships formed through adoption. His adoptive sister shares a special connection with him.
Pro Tip 2/3
Legality Implied
'Adoptive' hints at legal actions taken to form a familial bond, not just emotional commitment. After the court hearing, she became his legal adoptive mother.
Pro Tip 3/3
Beyond Bloodlines
'Adoptive' conveys that familial ties can be powerful and authentic without biological link. Their adoptive family supported them just as strongly as any biological family would.