sounds like you may need to use an if statement to display the usergroups in an array. I'm not a brilliant PHP coder, but something around this may suffice:
https://vborg.vbsupport.ru/showthread.php?t=246016
In lehmann's terms;
- Find all users in table users
- Select users with display group id's of (other usergroups excluding admin)
- If user has usergroup ID of admin do not show
- else show them