Hello Gambhir Kunwar,
Thank you for your post in this Q&A forum.
For your first question, We need a "region" field from MS Graph for a tenant. https://learn.microsoft.com/en-us/graph/api/managedtenants-tenantdetailedinformation-get?view=graph-rest-beta&tabs=http Is this end point stable to call?
This API still in beta version, the endpoint may be functional, it is not considered to be stable for production use. Definitely, not recommended to use for production.
For your second question;- do you want to know if you have multiple Global admin users with with mail object, with the endpoint retrieve all?