From opening paragraphs:
The guild hideout is divided into three sections: outer tunnels, which serve as the first line of defense against intruders; the living and working quarters for the thieves; and the inner sanctum, which only the elite members of the guild are allowed to access.
As the party moves through the dungeon, they will inevitably run into members of the guild. Depending on where they are at the time of the encounter, other members are likely to react to their presence.
While the party is in the outer tunnels, the thieves are content to allow the traps and hazards of the area to do their job. Once the party breaches the defenses and enters the living quarters, any thieves in the section will come to the aid of their guild mates.