I only have one Dumeril's so am no expert. Your snakes are beautiful, and don't look like any of the Madagascar/Dumeril crosses I've seen. Their colors/patterns are very strong and look classically Dumeril's to my eye. Sexual dimorphism in head size and shape exists in several snake species - I just don't know if Dumeril's are on that list, but that could partially explain what you are seeing.