How can i separate the dungeon "sectors" to avoid making all the monsters aggro by a single fight ?

First, make sure they are your own instances and not the vanilla monsters (just copy them for your own mod). You can reduce the aggro radius of the monsters and edit their wander package so they don't wander into each others' aggro area. Or, you can join them all to a friendly faction so they are allied to each other, but will still attack the player

Hi Paladinrider, i have applyed what you wrote, it works fine, better to do not build in Height, like a tower in that case
I would like to know if there is a way to do it by "REF", not only with monster NPC_ ?