Azure AD USERS management

Hi All,

I have a business case with one of my customers, currently there is a business collaboration between two entities and external entity scope is to create a users in the tenant on the other entity with specific naming convention and to manage small group of the created users, we will create an administrative unit for those group then will grant the admin user admin permission to manage this AU, but I still struggle with the user creation how can I grant this user a permission to manage the AU and to create those users with specific naming convention only?