I do not have time to give an extencive answer however references can have {{Tiddlername!!Fieldname}}
Your desire to show something in the sidebar adds complexity.
Also the currently visible tiddler sets <<currentTiddler>> this gets changed to name each subtiddler title one at a time in a list process unless you set a different variable=name in the list command, allowing currentTiddler to point to the parent.
Any tidder that is included in another can reference the parent tiddlers fields with the correct reference. I expect if you want to display the fields of another tiddler, the target, in the side bar you will have to save the name of the target tiddler somewhere like in a state tiddler the tiddler in the sidebar can use to reference its name and fields.
I susspect everything I have said is correct but may not help. lets see what others say.
Regards
Tony