With HPanel, you can create user and can assign as many as websites from different servers which you have and the user can manage those website files, databases, emails services within a single login. You can also provide them with different server level permissions.
You can update whitelabel settings at any point of time, so when your customer or team member logs into panel and need support from you then they can directly send you email from their dashboard and the support request will come to you for further investigation. If it's server level issues then you can assign the task to HPanel support.