Database permission for multiple users?

Hello, I have created 18 users and 5 groups in phpmyadmin for multiple projects management. In that case, I want to grant add, delete, edit permission to only specified users in any particular project. But in one project, I can not able to set edit routines permission for multiple users. Ex. If I give edit routines permission to User-1 and then again If I give same permission to User-2. After that User-1 will not have edit routines permission as it was transferred to User-2. Please guide me : How to set Edit Routine permission to Multiple Users. Thanking you in advance.