<!--base.html-->
{% block father %}

  {% block son %}
    son
  {% endblock %}

  {% block daughter %}
    daughter
  {% endblock %}

{% endblock %}

<!--page.html-->
{% extends 'base.html' %}
{% block son %}{% endblock %}

{% block father %}
  {{ block.super }}

  another guy

{% endblock %}
{% block daughter %}{{ block.super }}{% endblock %}