The Fall and Rise of House Dumbledore

Relations can have many forms.
There's the ones you share blood with but are not your family. They even can become your enemy.
Then there's the family you share blood with, they can be your biggest support. The ones that are always with you.
Then there's the family that are not your blood. The ones you find throughout your life. But the fact that you don't share the same blood doesn't make them any less family.

That says, blood doesn't always mean family and family doesn't always mean blood.