Hell's guardians could fight each other. They only recognized their master and their master's superiors, so even if the other side was a Devil, they would fight for their master.
However, this loyalty only lasted until the death of these members of Hell. The moment one in the position of competitor for the Throne of Hell died, their guardians and all possessions became ownerless. From then on, one could claim the right to sovereignty of these areas and underlings through a challenge called Soul Bleed.
Minos saw his undead of the same level as him advance against his opponent's stronger and more numerous undead, looking at the defiant and powerful gaze of the level 121 enemy.