Using a workspace may work in some instances. But I think what you are asking could be solved by additional functionality that could be requested for the Workspaces core plugin. It could be something that allows you to merge a workspace. This would mean that the notes from the merged workspace would simply be opened within the active tab group.
There is a chance something like this already exists as a community plugin, so it might be worth doing further searching. Regardless, I think what you’re asking about is probably of shared interest by others.
In the meantime, maybe you could just use workspaces as they currently are to achieve a less useful version of this. Another option would be to create a link-list note that you could open and pin. It would have a link to each of the desired notes with one per line to be clicked open. Either this or create a Templater script. Unfortunately I can’t help you there. However, it shouldn’t be too difficult. If that seems like a stretch, you could try creating a custom AutoHotkey or Keyboard Maestro macro to open each link in the note. Basically it would move the cursor to beginning of note, then repeat the following: arrow right twice, alt enter, arrow left twice, down arrow.
Just throwing some thoughts out there. I hope you find a good solution here on the forum. I would find it very useful. Thanks!