Two-Way Link between Cells (but trying to make it four-way)

The following code when pasted in the ThisWorkbook module keeps all sheets in a workbook in sync

Private Sub Workbook_SheetChange(ByVal Sh As Object, ByVal Target As Range)
Application.EnableEvents = False
For Each Cell In Target
    For Each Sheet In Sheets
        Sheet.Range(Cell.Address).Value = Cell.Value
    Next Sheet
Next Cell
Application.EnableEvents = True
End Sub

You may need to adapt this to restrict the range in which it operates.