Show the parent account's expiration for the child.

show_parent_expiration_date_for_child.php

<?php
/*
 * Show the parent account's expiration for the child in various places on frontend and admin pages in PMPro.
 *
 * You can add this recipe to your site by creating a custom plugin
 * or using the Code Snippets plugin available for free in the WordPress repository.
 * Read this companion article for step-by-step directions on either method.
 * https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/ 
 */
function replace_parent_expiration_for_child( $user_id ) {
	// Return if functions are not available.
	if ( ! function_exists( 'pmprosm_getSponsor' ) ) {
		return;
	}

	$sponsor = pmprosm_getSponsor( $user_id );
	if ( ! empty( $sponsor ) ) {
		$sponsor_level = pmpro_getMembershipLevelForUser( $sponsor->ID );
		$enddate = $sponsor_level->enddate;
		return $enddate;
	}
	return;
}

/**
 * Replaces the expiration text shown on the Membership Account page for the child account.
 *
 */
function use_parent_expiration_date_pmpro_account_membership_expiration_text( $expiration_text, $level ) {
	global $current_user;
	if ( function_exists( 'replace_parent_expiration_for_child' ) ) {
		$new_expiration_text = replace_parent_expiration_for_child( $current_user->ID );
		if ( ! empty( $new_expiration_text ) ) {
			$expiration_text = date_i18n( get_option( 'date_format' ), $new_expiration_text );
		}
	}
	return $expiration_text;
}
add_filter( 'pmpro_account_membership_expiration_text', 'use_parent_expiration_date_pmpro_account_membership_expiration_text', 10 , 2 );

/**
 * Replaces the expiration text shown on other areas, including places like the Membership Card or Members Directory.
 *
 */
function use_parent_expiration_date_pmpro_get_membership_level_for_user( $all_membership_levels, $user_id ) {
	if ( ! function_exists( 'replace_parent_expiration_for_child' ) ) {
		return $all_membership_levels;
	}

	$new_expiration_text = replace_parent_expiration_for_child( $user_id );
	if ( ! empty( $new_expiration_text ) ) {
		$all_membership_levels->enddate = $new_expiration_text;
	}

	return $all_membership_levels;
}
add_filter( 'pmpro_get_membership_level_for_user', 'use_parent_expiration_date_pmpro_get_membership_level_for_user', 10, 2 );

/**
 * Replaces the expiration text shown on the Members list in the WordPress admin.
 *
 */
function use_parent_expiration_date_pmpro_memberslist_expires_column( $expiration_text, $user_object ) {
	if ( function_exists( 'replace_parent_expiration_for_child' ) ) {
		$new_expiration_text = replace_parent_expiration_for_child( $user_object->ID );
		if ( ! empty( $new_expiration_text ) ) {
			$expiration_text = date_i18n( get_option( 'date_format' ), $new_expiration_text );
		}
	}
	return $expiration_text;
}
add_filter( 'pmpro_memberslist_expires_column', 'use_parent_expiration_date_pmpro_memberslist_expires_column', 10, 2);