At present Related Titles operate exactly as you have described.
LUV are aware that dealings with Related Titles requires improvement and are working on a solution. Unfortunately, I have no more information.
For now, if, for example, a Mortgage were to be registered on some but not all titles in a related titles set, then when it came to Discharge the Mortgage the dealing would need to be processed in paper as LUV have no way to support this anomaly via the electronic channel.
If some but not all titles in a related titles set were to be transferred via PEXA, Lodgement Verification would identify that not all titles in the related set were present in the dealing. In paper, I suspect the dealing set would not be accepted for lodgement, or would be the subject of a requisition.