family.rb

class Person

  def initialize(name, children = [])
    @children = children
    @descendents = []
    @name = name
  end

  def get_all_descendents

    children.each do |child|
      @descendents << child
      @descendents << child.get_all_descendents if child.children.size > 0
    end

    @descendents.flatten.uniq
  end

  def children
    @children || []
  end

  def to_s
    @name
  end

end

son = Person.new('Son')
father = Person.new('Father', [son])
grandfather = Person.new('GrandFather', [father])
granduncle = Person.new('GrandUncle', [])
great_grandfather = Person.new('GreatGrandfather', [grandfather, granduncle])

puts great_grandfather.get_all_descendents