How to check if a member (with a different prefix) is present under 2 hierarchies? Validation needed

Summary:

AC_Capital and AS_Capital are 2 siblings. Any member (AC_123) which is added to AC_Capital should also be added to AS_Capital. Requirement is to have it in the same viewpoint which is why I cannot create a separate viewpoint for this. Is there a way a validation that can be added to ensure the maintenance of the Alternate Hierarchies (albeit the member having a different prefix) ?

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