It might be available in the next version.
Faker::Relationship.familial #=> "Mother" or "Grandmother"
Faker::Relationship.familial('direct') #=> "Mother" or "Brother"
Faker::Relationship.familial('extended') #=> "Grandmother" or "Niece" or "Aunt"
Faker::Relationship.spouse #=> "Husband" or "Wife"
Faker::Relationship.parent #=> "Father" or "Mother"
Faker::Relationship.in_law #=> "Father-in-law"
Faker::Relationship.sibling #=> "Sister" or "Brother"