Why don't the npc all fight at once?

[Fabito48hd]

I have noticed, when generating melee fights between, for example, 10 people (5 vs 5), that not all of them enter into combat, but rather wait for a kind of turn, causing one to fight against all of them until they die, while the rest waiting.

I imagine that it is part of the game configuration to reduce the difficulty in combat.

Does anyone know if this can be changed and have the npc's enter the fight at the same time?

Any mod or something...

Thanks friends