Users without office 365 and licensing

I trying to help my customer's questions obout few issues.

His business doesn’t have office 365 but want to purchase PowerBI for 3 users.

1. Can they purchase and manage licenses without Office 365?
2. Do they need an Azure AD in that case?
3. One user will create the reports, and the other 2 will read them. Does all of them need Pro licenses? Can the readers use free?
   i read a licensing section on microsof documemts , but It's hard for me to understand because there are conflicting opinions.
   
   Thanks , Rita