How do I include a php file on a different cpanel account?

I have six cpanel accounts which all use the same code. I want to move all of this code to a seventh user. This would allow me to update the shared code for the 6 users at the same time. However, whenever I try to include a php file from the seventh user, I get a permission denied error. For example, 'require_once(/home/testuser/public_html/index.php)' results in the following warning: [19-Sep-2018 22:21:48 UTC] PHP Warning: require_once(/home/testuser/public_html/index.php): failed to open stream: Permission denied in /home//public_html/test.php on line 1 How can I fix this problem? Note: The index.php file has permissions 755.