B2B Direct Connect - ( Drap and Drop on teams and No Guest account)

You want three tenants to collaborate with native identities without guest objects. B2B Direct Connect supports that model only inside Teams shared channels; it is not a general replacement for guest access or external chats.

Configure reciprocal inbound and outbound B2B Direct Connect settings for each tenant pair, scope the allowed users and applications, and confirm Teams policies permit external shared-channel invitations. Create a shared channel in the host tenant and add the external users. They authenticate with their home tenants and can use channel chat, calls, apps, and files stored in the channel’s SharePoint site without guests.

For one-to-one or group external chat, External Access supports messaging and calling but not the same shared file workspace. Broader SharePoint or OneDrive sharing commonly uses B2B collaboration and guest identities. Therefore, this cannot coexist with a strict no-guest rule: use shared channels, or accept guests where broader resource sharing is required.