I think Sessa's reason for running to Carmine to tell him about Orena's plans for a coup was more self serving than out of loyalty to Persico. Sessa probably figured his position and power in the family will increase under Persico if he gets Orena whacked. Sessa probably also calculated that his future looked dim if Orena became official boss and Orena would probably have him removed as consigliere somewhere down the line and replaced with a more qualified consigliere.