Groups and subgroups for permission

First you need to make group and subgroup. You can use wordpress existing User Role or you can make custom user role (group) by own. Members is a nice plugin to create custom role.

For example your main group is “Group1” and subgroup is “Subgroup1”. First you need to check current user role (Group of user). After that you can show full content for “Group1”. And first paragraph for Subgroup1 group, I think use excerpt is the best solution.

So full code should be like.

<?php
global $current_user;
$current_user = array_shift($current_user->roles);

if ( have_posts() ) : while ( have_posts() ) : the_post(); ?>
    <h1><?php the_title(); ?></h1>
    <?php 
        if($current_user == 'group1') {
            the_content();
        }elseif ($current_user == 'subgroup1') {
            the_excerpt();
        }else {
            // if user is not under group1 or subgroup1 
            // you can do here what you like
            // For example redirec home page. Or show message please register
        }
    ?>
<?php endwhile; endif; ?>