Bi-Directional Data Entry

I want to create a Excel file with three worksheets, where each wprksheet contains a large table. While most of the cells' content is unique, several dozen of the cells' content will appear at different places in all two, or all three, worksheets.

The table is very simple for all of the cells whose content is unique. My question has to do with the cells whose content is duplicated in two or all three worksheets. For these cells, I could just force the user to go to a 'input'' worksheet and enter changes from there. That is very simple to implement.
However, to make updates simple for the user (even though the spreadsheet becomes more complex for me), I don't want to force a user who is making updates on one worksheet to have to go to another worksheet to change values for cells whose content appears in multiple worksheets. Instead, I want a user to be able to enter a new value into any cell of any worksheet and, if that cell's content appears in multiple worksheets, for that value to appear in that cell's location on the other worksheet(s).

Normally, I follow the description of what I'm trying to do with a copy of the code I've been working on. In this case, I don't have any code because I can't figure out how to do this. Despite my lack of ideas on how to do this, and despite my inability to find a solution by searching this site and the internet in general, I am confident that someone with better VBA skills than me can tell me how to do this - even for several dozen cells scattered across three worksheets. The question is 'how', so I'm reaching out for suggestions.

Thank you in advance for your help on this, as I am completely stymied.