How does SQL Server Merge Replication maintain referential integrity?
Review How Merge Replication Detects and Resolves Conflicts 

A lineage column is used which contains the generation and the node that made the change.  The actual winner decision during the conflict depends upon the conflict resolver used for the article. Using the default prority-based resolver, a priority value per node should be assigned per subscriber to determine the winner for all conflicts.

With regards to referential integrity and the concept of conflict resolution in mind, the processing order with which tables (articles) are processed is your only means of guiding the conflict resolution before your child tables.  You can modify the order of the article processing in the merge publication via the @processing_order parameter for sp_addmergearticle