B. Billing is based on owners and members of GitHub organizations.
This describes the billing model for a standard GitHub Enterprise Cloud plan, not one configured with Enterprise Managed Users (EMU).
C. Billing is based on total users in the enterprise that are not dormant.
A provisioned managed user consumes a license regardless of their activity status. To free up a license, the user must be deprovisioned via the identity provider.
D. Billing is based on the number of users created in Azure AD.
Billing is based only on the users from Azure AD (or another IdP) that are specifically provisioned for access to the GitHub Enterprise, not the total number of users in the entire IdP tenant.