Hi,
For servers without Session Host roles, it only allow two remote session at the same time, otherwise, RDSH role with RDS CAL is needed.
From server manager in the servers, it will provide feature for users to perform some actions remotely in Server B, if they logged in Server A. For RSAT, similar functions will achieved when users logged in Clients like windows 10 but want to perform actions in Servers.
Moreover, a RDS configuration without RD connection broker does not provide access to all RDS functionality, including access to RemoteApp programs or the RDWeb website. Guidance to deploy RDS without RDCB are followed as below:
https://learn.microsoft.com/en-us/troubleshoot/windows-server/remote/install-rds-host-role-service-without-connection-broker
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Hope this helps and please help to accept as Answer if the response is useful.
Thanks,
Jenny