Validation for overlapping dates among siblings

I'm using Financial Reporting Studio 11.1.2.3 and have a requirement to implement a validation that checks if level 0 entities have overlapping dates (2 date members that define a range are defined in another dimension). The edit should only check dates among the groups of level 0 siblings; i.e., if there are 100 parents with between 1-10 level 0 siblings each, then first check for overlaps among the first group of siblings, then the next, and so on.

The solution should be dynamic so that no changes will be required if/when the number of parents or siblings change. Any ideas on how to implement this in Financial Reporting Studio?