I'm faced with an Office 365 tenant to tenant migration involving 3 tenancies. B & C will be migrating into tenant A. Please see below image of the existing setup. All identities live in the same AD DOMAIN, but are using different UPNs and 3 AD connect servers.
Before the data migration phase (the easy part), I will need to create new identities for people who live in tenant B in tenant A. How do I go about this seeing as all accounts are living in the same AD domain/forest?
What would be the best approach here to handle the identies and the least amount of disruption to users?