example.rb

module TestParent
  class Library
    def name
      "Oxford"
    end  
  end  
   
   class Book
    def library
       Library.new
    end  
  end  
end  

module Child
  class Library < TestParent::Library
    def name
      "Child Library"
    end  
  end
  
  class Book < TestParent::Book
    # any way to avoid having to recreate the method to reset the class scope? 
    def library
      Library.new
    end 
  end  
end  

module TestParent
  module SharedMethods
    def library
      Library.new
    end  
  end

  class Library
    def name
      "Oxford"
    end  
  end  

  class Book
    include SharedMethods
  end
end  

module Child
  class Library < TestParent::Library
    def name
      "Child Library"
    end  
  end

  class Book < TestParent::Book
    include TestParent::SharedMethods
  end  
end