REdhat recommends rather than modifying the sudioers file itself you and entries to the /etc/sudoers.d/ directory

Permissions are similar for example

[student@servera ~]$ sudo cat /etc/sudoers.d/operator1
operator1 ALL=(ALL) ALL

Here is how you would create file to grant sudo permissions for the Admin group

echo "%admin ALL=(ALL) ALL" >> /etc/sudoers.d/admin