Unless there is an obvious power difference between two nobles, whoever is in the dominant position depends on context, reputation, experience, charisma, leverage, etc. Oftentimes things are unclear, and your nobles will end up butting heads. Other nobles would then start taking sides or try to mediate. Now you have full-blown intra-realm conflict. This is all by design.
Your nobles will simply have to figure out their pecking order, like adults do in the real world.