Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
Dear mongojimmy,
Good day!
Thank you for posting to Microsoft Community. We are glad to assist.
As per your mentioned description about "Subsidiary Tenant". Based on my knowledge if tenants 1 and 2 are separate, settings and licenses will be separate and cannot be mixed use unless like they have 1.com and 2.com. they can merge into one tenant. Yet same tenant cannot be distinct entities.
However, you may check with Azure AD B2B collaboration overview - Microsoft Entra | Microsoft Learn if it can provide any suitable information about your mentioned concern. Kindly Keep in mind that B2B collaboration and B2B direct connect are designed for collaboration between organizations, and not for merging or consolidating tenants. You will still need to manage each tenant separately, including licensing, billing, and management.
In the meantime, I would like to share some information with you, Microsoft has specific dedicated support channel for certain different aspect and attributes, would you mind to also post your concern on our specific Microsoft Q&A forum community for certain different support scope? Our relevant community members can further provide you possible information from their side. Here is that dedicated forum community to place your concern: Microsoft Q&A
Thanks for your understanding! Your patience and cooperation will be highly appreciated. Have a nice day!
Best regards,
Inema | Microsoft Community Moderator