How to add page content into another page

You can do this but before I tell you how I have to express a concern. You will have severe duplicate content problems if all of your pages are the same except for that <h2> tag.

Now, what you need to do is create a Custom Page Template, with the following:

<?php
/*
Template Name: Venue Duplicate Content Template
*/
get_header();

$special_content = new WP_Query(array('p' => 675,'post_type'=>'page'));

if (have_posts()) {
  while(have_posts()) {
    the_post();
    the_title(); // add your <h2> tag or whatever other markup you want.
    $special_content->the_post();
    the_content();
  }
}

Edit the ID to match the page with the “real” content, of course.

When you create your individual wedding-(venue name) pages, just select that template as the “Template”