Your idea is such bad practice that Excel pointedly doesn't support it. This lack of support is demonstrated by the fact that the Worksheet_Change event isn't triggered by a change induced programmatically from an outside source.
Therefore you must rely on the capabilities of the macro in workbook A to make all the required changes in B and C. As mirror image: Don't try to trigger macros in workbooks B and C from a macro in workbook A.
However, it is possible for a macro in workbook A to call macros in workbooks B and C. The difference is in who retains control. So, your updating macro in workbook A could first update workbooks B and C and then call macros in those workbooks that process the updates.
The question to answer is what advantage can be derived from not having these macros all in workbook A. I point to the cost. Since the dependent workbooks are controlled independently (otherwise they wouldn't be separate) circumstances may interfere with access and intended updates may not happen. If the code were in workbook A problems can easily be reported. If the code resides in remote workbooks reporting of irregularities is much, much more complicated.