adoptive
Describing parents or family joined by adoption, not birth.
Adoptive describes the relationship created through adoption rather than through birth. When parents adopt a child who wasn't born to them, they become that child's adoptive parents, and the child becomes their adoptive son or adoptive daughter. The family bonds are just as real and strong as any other family; they simply began differently.
You might read about someone's adoptive family or adoptive home. These terms simply explain how the family formed. An adoptive parent has all the same responsibilities, joys, and challenges as any other parent: helping with homework, celebrating birthdays, worrying about scraped knees, and supporting their child's dreams.
Many families form this way. Some children are adopted as babies, others when they're older. Some adoptive parents already have children born to them, while others build their entire family through adoption.
People sometimes think they need to constantly point out that a family is adoptive, but most families just consider themselves families. The word adoptive is mainly useful when the specific details of how a family formed actually matter to the conversation, like in legal documents or when telling someone's personal story.